RFR: JDK-8267163: Rename anonymous loader tests to hidden loader tests

[Mikhailo Seledtsov]

Please review this simple change that renames vm/mlvm tests and test package name from anonymous to hidden.
Testing:
  Ran open/test/hotspot/jtreg/vmTestbase/vm/mlvm on MacOS-x64: PASS
  Running open/test/hotspot/jtreg/vmTestbase/vm/mlvm on multiple platforms: in progress ...

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Commit messages:
 - Renamed AnonkTestee* to HiddenkTestee*
 - Renamed package name except for VM testbase conversion comment
 - Renamed Anonk classes
 - Renamed classes
 - Renamed anonloader to hiddenloader

Changes: https://git.openjdk.java.net/jdk/pull/5570/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5570&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267163
  Stats: 1268 lines in 21 files changed: 631 ins; 631 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5570.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5570/head:pull/5570

PR: https://git.openjdk.java.net/jdk/pull/5570