RFR: 8256063: Module::getPackages on an unnamed module may return packages that are in a named module

[Mandy Chung]

If `Module::getPackages` is invoked on the unnamed module of a class loader
then the set of packages returned will include the packages of any named modules
that are defined to that class loader.  This is a spec and implementation bug.

`Module::getPackages` is changed to return the packages that are defined in
the unnamed module. 

CSR: https://bugs.openjdk.java.net/browse/JDK-8256242

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

Commit messages:
 - add new regression test
 - 8256063: Module::getPackages on an unnamed module may return packages that are in a named module

Changes: https://git.openjdk.java.net/jdk/pull/1178/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1178&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256063
  Stats: 123 lines in 4 files changed: 118 ins; 1 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1178.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1178/head:pull/1178

PR: https://git.openjdk.java.net/jdk/pull/1178