Update StructuredSwiftRepresentation (#1725)

Motivation:

The latest version of the Code Renderer uses the Expression type for the `left` property of
a VariableDescription, so we need to also update the StructuredSwiftRepresentation accordingly.

Result:

We will have the latest version of StructuredSwiftRepresentation for the new CodeGenLib.

Sources/GRPCCodeGen/Internal/StructuredSwiftRepresentation.swift

@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the SwiftOpenAPIGenerator open source project
@@ -66,11 +65,14 @@ struct ImportDescription: Equatable, Codable {
 /// A description of an access modifier.
 ///
 /// For example: `public`.
-enum AccessModifier: String, Equatable, Codable {
+internal enum AccessModifier: String, Sendable, Equatable, Codable {
 
   /// A declaration accessible outside of the module.
   case `public`
 
+  /// A declaration accessible outside of the module but only inside the containing package or project.
+  case `package`
+
   /// A declaration only accessible inside of the module.
   case `internal`
 
@@ -256,7 +258,7 @@ struct VariableDescription: Equatable, Codable {
   /// The name of the variable.
   ///
   /// For example, in `let foo = 42`, `left` is `foo`.
-  var left: String
+  var left: Expression
 
   /// The type of the variable.
   ///
@@ -1126,6 +1128,49 @@ extension Declaration {
     setter: [CodeBlock]? = nil,
     modify: [CodeBlock]? = nil
 
+  ) -> Self {
+    .variable(
+      accessModifier: accessModifier,
+      isStatic: isStatic,
+      kind: kind,
+      left: .identifierPattern(left),
+      type: type,
+      right: right,
+      getter: getter,
+      getterEffects: getterEffects,
+      setter: setter,
+      modify: modify
+    )
+  }
+
+  /// A variable declaration.
+  ///
+  /// For example: `let foo = 42`.
+  /// - Parameters:
+  ///   - accessModifier: An access modifier.
+  ///   - isStatic: A Boolean value that indicates whether the variable
+  ///   is static.
+  ///   - kind: The variable binding kind.
+  ///   - left: The name of the variable.
+  ///   - type: The type of the variable.
+  ///   - right: The expression to be assigned to the variable.
+  ///   - getter: Body code for the getter of the variable.
+  ///   - getterEffects: Effects of the getter.
+  ///   - setter: Body code for the setter of the variable.
+  ///   - modify: Body code for the `_modify` accessor.
+  /// - Returns: Variable declaration.
+  static func variable(
+    accessModifier: AccessModifier? = nil,
+    isStatic: Bool = false,
+    kind: BindingKind,
+    left: Expression,
+    type: ExistingTypeDescription? = nil,
+    right: Expression? = nil,
+    getter: [CodeBlock]? = nil,
+    getterEffects: [FunctionKeyword] = [],
+    setter: [CodeBlock]? = nil,
+    modify: [CodeBlock]? = nil
+
   ) -> Self {
     .variable(
       .init(
@@ -1573,15 +1618,6 @@ extension MemberAccessDescription {
   static func dot(_ member: String) -> Self { .init(right: member) }
 }
 
-extension Expression: ExpressibleByStringLiteral, ExpressibleByNilLiteral, ExpressibleByArrayLiteral
-{
-  init(arrayLiteral elements: Expression...) { self = .literal(.array(elements)) }
-
-  init(stringLiteral value: String) { self = .literal(.string(value)) }
-
-  init(nilLiteral: ()) { self = .literal(.nil) }
-}
-
 extension LiteralDescription: ExpressibleByStringLiteral, ExpressibleByNilLiteral,
   ExpressibleByArrayLiteral
 {
@@ -1599,14 +1635,18 @@ extension VariableDescription {
   /// For example `var foo = 42`.
   /// - Parameter name: The name of the variable.
   /// - Returns: A new mutable variable declaration.
-  static func `var`(_ name: String) -> Self { Self.init(kind: .var, left: name) }
+  static func `var`(_ name: String) -> Self {
+    Self.init(kind: .var, left: .identifierPattern(name))
+  }
 
   /// Returns a new immutable variable declaration.
   ///
   /// For example `let foo = 42`.
   /// - Parameter name: The name of the variable.
   /// - Returns: A new immutable variable declaration.
-  static func `let`(_ name: String) -> Self { Self.init(kind: .let, left: name) }
+  static func `let`(_ name: String) -> Self {
+    Self.init(kind: .let, left: .identifierPattern(name))
+  }
 }
 
 extension Expression {
@@ -1618,10 +1658,6 @@ extension Expression {
   func equals(_ rhs: Expression) -> AssignmentDescription { .init(left: self, right: rhs) }
 }
 
-extension FunctionArgumentDescription: ExpressibleByStringLiteral {
-  init(stringLiteral value: String) { self = .init(expression: .literal(.string(value))) }
-}
-
 extension FunctionSignatureDescription {
   /// Returns a new function signature description that has the access
   /// modifier updated to the specified one.