RFR: 8284942: Proxy building can just iterate superinterfaces once [v6]

[liach]

> Currently, in ProxyBuilder::mapToModule and ProxyBuilder::defineProxyClass, the interfaces are iterated twice. The two passes can be merged into one, yielding the whole proxy definition context (module, package, whether there's package-private interface) when determining the module.
> 
> Split from #8278. Helpful for moving proxies to hidden classes, but is a good cleanup on its own.

liach has updated the pull request incrementally with one additional commit since the last revision:

  Fixes suggested by mandy

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8281/files
  - new: https://git.openjdk.java.net/jdk/pull/8281/files/20edc525..9d7ebaab

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8281&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8281&range=04-05

  Stats: 13 lines in 1 file changed: 4 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8281.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8281/head:pull/8281

PR: https://git.openjdk.java.net/jdk/pull/8281