Add kdoc for functionDeclarations

Author: rlazo

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

@@ -24,6 +24,12 @@ package com.google.firebase.vertexai.type
  */
 class Tool internal constructor(internal val functionDeclarations: List<FunctionDeclaration>?) {
   companion object {
+
+    /**
+     * Creates a [Tool] instance that provides the model with access to the [functionDeclarations].
+     *
+     * @param functionDeclarations The list of functions that this tool allows the model access to.
+     */
     @JvmStatic
     fun functionDeclarations(functionDeclarations: List<FunctionDeclaration>): Tool {
       return Tool(functionDeclarations)