[Vertex AI] Add Imagen warning for invalid JPEG compression quality (#14440)

Author: andrewheard

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

@@ -45,6 +45,12 @@ public struct ImagenImageFormat {
   ///     compression (lowest image quality, smallest file size) and `100` is the lowest level of
   ///     compression (highest image quality, largest file size); defaults to `75`.
   public static func jpeg(compressionQuality: Int? = nil) -> ImagenImageFormat {
+    if let compressionQuality, compressionQuality < 0 || compressionQuality > 100 {
+      VertexLog.warning(code: .imagenInvalidJPEGCompressionQuality, """
+      Invalid JPEG compression quality of \(compressionQuality) specified; the supported range is \
+      [0, 100].
+      """)
+    }
     return ImagenImageFormat(mimeType: "image/jpeg", compressionQuality: compressionQuality)
   }
 }

FirebaseVertexAI/Sources/VertexLog.swift

@@ -31,9 +31,12 @@ enum VertexLog {
     // API Enablement Errors
     case vertexAIInFirebaseAPIDisabled = 200
 
-    // Model Configuration
+    // Generative Model Configuration
     case generativeModelInitialized = 1000
 
+    // Imagen Model Configuration
+    case imagenInvalidJPEGCompressionQuality = 1201
+
     // Network Errors
     case generativeAIServiceNonHTTPResponse = 2000
     case loadRequestResponseError = 2001