Move sun.misc.ProxyGenerator to jdk.internal.reflect

No new code here, just giving sun.misc.ProxyGenerator a more appropriate location, in jdk.internal.reflect
( since it contains the code to generate a dynamic proxy class for the java.lang.reflect.Proxy ).

http://cr.openjdk.java.net/~chegar/proxyGeneratorWebrev/webrev/

Note: ProxyGenerator could be moved into java.lang.reflect, as a package-private class, but I see no
reason to move it into an exported package, and a package that it not on the restricted package list.