RFR JDK-8022795: Method.isVarargs of dynamic proxy generated method to match the proxy interface method

[Mandy Chung]

Webrev:
http://cr.openjdk.java.net/~mchung/jdk16/webrevs/8022795/webrev.00/

A small improvement to the dynamic proxy generated method to have
ACC_VARARGS matching the method declared in a proxy interface if set.
If there are two or more proxy interfaces declaring such a method,
it matches the method declared in the first proxy interface.

thanks
Mandy