[Vertex AI] Replace ImagenImage protocol with _ImagenImage struct

Author: andrewheard

FirebaseVertexAI/Sources/Types/Internal/Imagen/InternalImagenImage.swift

@@ -27,8 +27,8 @@ public struct ImagenFileDataImage {
 
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 extension ImagenFileDataImage: ImagenImageRepresentable {
-  public var imagenImage: any ImagenImage {
-    InternalImagenImage(mimeType: mimeType, bytesBase64Encoded: nil, gcsURI: gcsURI)
+  public var _imagenImage: _ImagenImage {
+    _ImagenImage(mimeType: mimeType, bytesBase64Encoded: nil, gcsURI: gcsURI)
   }
 }
 

FirebaseVertexAI/Sources/Types/Public/Imagen/ImagenFileDataImage.swift

@@ -15,8 +15,8 @@
 import Foundation
 
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
-public protocol ImagenImage: ImagenImageRepresentable {
-  var mimeType: String { get }
-  var bytesBase64Encoded: String? { get }
-  var gcsURI: String? { get }
+public struct _ImagenImage {
+  let mimeType: String
+  let bytesBase64Encoded: String?
+  let gcsURI: String?
 }

FirebaseVertexAI/Sources/Types/Public/Imagen/ImagenImage.swift

@@ -16,12 +16,5 @@ import Foundation
 
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 public protocol ImagenImageRepresentable {
-  var imagenImage: any ImagenImage { get }
-}
-
-@available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
-public extension ImagenImage {
-  var imagenImage: any ImagenImage {
-    return self
-  }
+  var _imagenImage: _ImagenImage { get }
 }

FirebaseVertexAI/Sources/Types/Public/Imagen/ImagenImageRepresentable.swift

@@ -31,8 +31,8 @@ public struct ImagenInlineDataImage {
 
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 extension ImagenInlineDataImage: ImagenImageRepresentable {
-  public var imagenImage: any ImagenImage {
-    InternalImagenImage(
+  public var _imagenImage: _ImagenImage {
+    _ImagenImage(
       mimeType: mimeType,
       bytesBase64Encoded: data.base64EncodedString(),
       gcsURI: nil