fix: prevent unchecked warnings in gax-httpjson [gax-java]

gax-httpjson/src/main/java/com/google/api/gax/httpjson/ApiMessageHttpRequestFormatter.java

@@ -75,6 +75,7 @@ ApiMessageHttpRequestFormatter.Builder<RequestT> newBuilder() {
     return new ApiMessageHttpRequestFormatter.Builder<>();
   }
 
+  @SuppressWarnings("unchecked")
   @Override
   public Map<String, List<String>> getQueryParamNames(RequestT apiMessage) {
     Set<String> paramNames = getQueryParamNames();

gax-httpjson/src/main/java/com/google/api/gax/httpjson/ApiMethodDescriptor.java

@@ -50,7 +50,7 @@ public abstract class ApiMethodDescriptor<RequestT, ResponseT> {
   public abstract String getHttpMethod();
 
   public static <RequestT, ResponseT> Builder<RequestT, ResponseT> newBuilder() {
-    return new AutoValue_ApiMethodDescriptor.Builder();
+    return new AutoValue_ApiMethodDescriptor.Builder<RequestT, ResponseT>();
   }
 
   @AutoValue.Builder