Proxy::newProxyInstance spec should specify the behavior if a given proxy interface is hidden

Summary

Update the spec of Proxy::newProxyInstance to specify `IllegalArgumentException thrown if a given proxy interface is hidden.

Problem

The current spec of Proxy::newProxyInstance throws IAE if a given proxy interface cannot be found by the given class loader. This covers for the case of a hidden proxy interface since it is not discoverable by any class loader. It should explicitly list in the restrictions section that the given interfaces must be non-hidden interfaces.

Solution

Update the spec of Proxy::newProxyInstance to require all proxy interfaces be non-hidden. There is no behavioral change. The current implementation already throws IAE if any one of the given interfaces is hidden.

Specification

Update the spec of Proxy::newProxyInstance

      * <a id="restrictions">{@code IllegalArgumentException} will be thrown
      * if any of the following restrictions is violated:</a>
      * <ul>
      * <li>All of {@code Class} objects in the given {@code interfaces} array
-     * must represent interfaces, not classes or primitive types.
+     * must represent {@linkplain Class#isHidden() non-hidden} interfaces,
+     * not classes or primitive types.