added java interop layer annotation

Author: David Motsonashvili

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/ImagenModel.kt

@@ -128,6 +128,7 @@ internal constructor(
   }
 }
 
+@OptIn(PublicPreviewAPI::class)
 private fun ImagenGenerationResponse.Internal.validate(): ImagenGenerationResponse.Internal {
   if (predictions.none { it.mimeType != null }) {
     throw ContentBlockedException(

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/java/ImagenModelFutures.kt

@@ -19,6 +19,7 @@ package com.google.firebase.vertexai.java
 import androidx.concurrent.futures.SuspendToFutureAdapter
 import com.google.common.util.concurrent.ListenableFuture
 import com.google.firebase.vertexai.ImagenModel
+import com.google.firebase.vertexai.common.PublicPreviewAPI
 import com.google.firebase.vertexai.type.ImagenGCSImage
 import com.google.firebase.vertexai.type.ImagenGenerationResponse
 import com.google.firebase.vertexai.type.ImagenInlineImage
@@ -28,6 +29,7 @@ import com.google.firebase.vertexai.type.ImagenInlineImage
  *
  * @see [ImagenModel]
  */
+@OptIn(PublicPreviewAPI::class)
 public abstract class ImagenModelFutures internal constructor() {
   /**
    * Generates an image, returning the result directly to the caller.