add GenerativeContentResponse#functionCalls (#5931)

Author: davidmotson

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/GenerateContentResponse.kt

@@ -33,10 +33,14 @@ class GenerateContentResponse(
   /** Convenience field representing the first text part in the response, if it exists. */
   val text: String? by lazy { firstPartAs<TextPart>()?.text }
 
-  /** Convenience field representing the first text part in the response, if it exists. */
-  val functionCall: FunctionCallPart? by lazy { firstPartAs() }
+  /** Convenience field to get all the function call parts in the request, if they exist */
+  val functionCalls: List<FunctionCallPart> by lazy {
+    candidates.first().content.parts.filterIsInstance<FunctionCallPart>()
+  }
 
-  /** Convenience field representing the first text part in the response, if it exists. */
+  /**
+   * Convenience field representing the first function response part in the response, if it exists.
+   */
   val functionResponse: FunctionResponsePart? by lazy { firstPartAs() }
 
   private inline fun <reified T : Part> firstPartAs(): T? {