Move the Generating-stubs article to grpc-swift-protobuf (#2180)

Motivation:

It makes more sense for it to live there.

Modifications:

- Delete the contents and point to its new home on the Swift Package
Index.

Result:

Docs live in a more sensible place.

Sources/GRPCCore/Documentation.docc/Articles/Generating-stubs.md

@@ -1,169 +1,8 @@
-# Generating stubs
+# Generating stubs with gRPC Swift Protobuf
 
 Learn how to generate stubs for gRPC Swift from a service defined using the Protocol Buffers IDL.
 
 ## Overview
 
-If you've used Protocol Buffers before then generating gRPC Swift stubs should be simple. If you're
-unfamiliar with Protocol Buffers then you should get comfortable with the concepts before
-continuing; the [Protocol Buffers website](https://protobuf.dev/) is a great place to start.
-
-You can use the `protoc` plugin from the command line directly, or you can make use of a 
- [Swift Package Manager build plugin](https://github.com/swiftlang/swift-package-manager/blob/main/Documentation/Plugins.md) 
-convenience which adds the stub generation to the Swift build graph.
-You may use the build plugin either from the command line or from Xcode.
-
-## Using the build plugin
-
-The build plugin (`GRPCProtobufGenerator`) is a great choice for convenient dynamic code generation, however it does come with some limitations.
-Because it generates the gRPC Swift stubs as part of the build it has the requirement that `protoc` must be available 
-at compile time. This requirement means it is not a good fit for library authors who do not have
-direct control over this.
-
-The build plugin detects `.proto` files in the source tree and invokes `protoc` once for each file 
-(caching results and performing the generation as necessary).
-
-### Adoption
-You must adopt Swift Package Manager build plugins on a per-target basis by modifying your package manifest 
-(`Package.swift` file). To do this, declare the grpc-swift-protobuf package as a dependency and add the plugin 
-to your desired targets.
-
-For example, to make use of the plugin for generating gRPC Swift stubs as part of the 
-`echo-server` target:
-```swift
-targets: [
-   .executableTarget(
-     name: "echo-server",
-     dependencies: [
-       // ...
-     ],
-     plugins: [
-       .plugin(name: "GRPCProtobufGenerator", package: "grpc-swift-protobuf")
-     ]
-   )
- ]
-```
-Once this is done you need to ensure that the `.proto` files to be used for generation 
-are included in the target's source directory and that you have defined at least one configuration file.
-
-### Configuration
-
-You must provide a configuration file in the directory which encloses all `.proto` files (in the same directory or a parent). 
-Configuration files, written in JSON, tell the build plugin about the options used for `protoc` invocations. 
-You must name the file `grpc-swift-proto-generator-config.json` and structure it in the following format:
-```json
-{
-  "generate": {
-    "clients": true,
-    "servers": true,
-    "messages": true,
-  },
-  "generatedSource": {
-    "accessLevelOnImports": false,
-    "accessLevel": "internal",
-  }
-  "protoc": {
-    "executablePath": "/opt/homebrew/bin/protoc"
-    "importPaths": [
-      "../directory_1",
-    ],
-  },
-}
-```
-
-The options do not need to be specified and each have default values.
-
-| Name                                   | Possible Values                            | Default      | Description                                         |
-|----------------------------------------|--------------------------------------------|--------------|-----------------------------------------------------|
-| `generate.servers`                     | `true`, `false`                            | `true`       | Generate server stubs                               |
-| `generate.clients`                     | `true`, `false`                            | `true`       | Generate client stubs                               |
-| `generate.messages`                    | `true`, `false`                            | `true`       | Generate message stubs                              |
-| `generatedSource.accessLevelOnImports` | `true`, `false`                            | `false`      | Whether imports should have explicit access levels  |
-| `generatedSource.accessLevel`          | `"public"`, `"package"`, `"internal"`      | `"internal"` | Access level for generated stubs                    |
-| `protoc.executablePath`                | N/A                                        | `null`†      | Path to the `protoc` executable                     |
-| `protoc.importPaths`                   | N/A                                        | `null`‡      | Import paths passed to `protoc`                     |
-
-† The Swift Package Manager build plugin infrastructure will attempt to discover the executable's location if you don't provide one.
-
-‡ If you don't provide any import paths then the path to the configuration file will be used on a per-source-file basis. 
-
-Many of these options map to `protoc-gen-grpc-swift` and `protoc-gen-swift` options.
-
-If you require greater flexibility you may specify more than one configuration file.
-Configuration files apply to all `.proto` files equal to or below it in the file hierarchy. A configuration file
-lower in the file hierarchy supersedes one above it.
-
-### Using protoc
-
-The [`grpc-swift-protobuf`](https://github.com/grpc/grpc-swift-protobuf) package provides
-`protoc-gen-grpc-swift`, a program which is a plugin for the Protocol Buffers compiler, `protoc`.
-To generate gRPC stubs for your `.proto` files directly you must run the `protoc` command with
-the `--grpc-swift_out=<DIRECTORY>` option:
-
-```console
-protoc --grpc-swift_out=. my-service.proto
-```
-
-> `protoc-gen-grpc-swift` only generates gRPC stubs, it doesn't generate messages. You must use
-> `protoc-gen-swift` to generate messages in addition to gRPC Stubs.
-
-The presence of `--grpc-swift_out` tells `protoc` to use the `protoc-gen-grpc-swift` plugin. By
-default it'll look for the plugin in your `PATH`. You can also specify the path to the plugin
-explicitly:
-
-```console
-protoc --plugin=/path/to/protoc-gen-grpc-swift --grpc-swift_out=. my-service.proto
-```
-
-You can also specify various option the `protoc-gen-grpc-swift` via `protoc` using
-the `--grpc-swift_opt` argument:
-
-```console
-protoc --grpc-swift_opt=<OPTION_NAME>=<OPTION_VALUE> --grpc-swift_out=.
-```
-
-You can specify multiple options by passing the `--grpc-swift_opt` argument multiple times:
-
-```console
-protoc \
-  --grpc-swift_opt=<OPTION_NAME1>=<OPTION_VALUE1> \
-  --grpc-swift_opt=<OPTION_NAME2>=<OPTION_VALUE2> \
-  --grpc-swift_out=.
-```
-
-#### Generator options
-
-| Name                      | Possible Values                            | Default    | Description                                              |
-|---------------------------|--------------------------------------------|------------|----------------------------------------------------------|
-| `Visibility`              | `Public`, `Package`, `Internal`            | `Internal` | Access level for generated stubs                         |
-| `Server`                  | `True`, `False`                            | `True`     | Generate server stubs                                    |
-| `Client`                  | `True`, `False`                            | `True`     | Generate client stubs                                    |
-| `FileNaming`              | `FullPath`, `PathToUnderscore`, `DropPath` | `FullPath` | How generated source files should be named. (See below.) |
-| `ProtoPathModuleMappings` |                                            |            | Path to module map `.asciipb` file. (See below.)         |
-| `UseAccessLevelOnImports` | `True`, `False`                            | `False`    | Whether imports should have explicit access levels.      |
-
-The `FileNaming` option has three possible values, for an input of `foo/bar/baz.proto` the following
-output file will be generated:
-- `FullPath`: `foo/bar/baz.grpc.swift`.
-- `PathToUnderscore`: `foo_bar_baz.grpc.swift`
-- `DropPath`: `baz.grpc.swift`
-
-The code generator assumes all inputs are generated into the same module, `ProtoPathModuleMappings`
-allows you to specify a mapping from `.proto` files to the Swift module they are generated in. This
-allows the code generator to add appropriate imports to your generated stubs. This is described in
-more detail in the [SwiftProtobuf documentation](https://github.com/apple/swift-protobuf/blob/main/Documentation/PLUGIN.md).
-
-#### Building the protoc plugin
-
-> The version of `protoc-gen-grpc-swift` you use mustn't be newer than the version of
-> the `grpc-swift-protobuf` you're using.
-
-If your package depends on `grpc-swift-protobuf` then you can get a copy of `protoc-gen-grpc-swift`
-by building it directly:
-
-```console
-swift build --product protoc-gen-grpc-swift
-```
-
-This command will build the plugin into `.build/debug` directory. You can get the full path using
-`swift build --show-bin-path`.
+You can learn about generating gRPC stubs from the [gRPC Swift Protobuf 
+documentation](https://swiftpackageindex.com/grpc/grpc-swift-protobuf/documentation/grpcprotobuf/generating-stubs).