RFR: 8328821: Map.of().entrySet() mutators should throw UnsupportedOperationException [v4]

[Liam Miller-Cushon]

> This change overrides mutator methods in the implementation returned by `Map.of().entrySet()` to throw `UnsupportedOperationException`.

Liam Miller-Cushon has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:

 - Also throw UOE for mutators on keySet() and values()
   
   and add more test coverage to MOAT.
 - Merge remote-tracking branch 'origin/master' into JDK-8328821-make-clear-consistent
 - Merge remote-tracking branch 'origin/master' into JDK-8328821-make-clear-consistent
 - Check m.entrySet().hashCode() in MOAT
 - Merge remote-tracking branch 'origin/master' into JDK-8328821-make-clear-consistent
 - Use AbstractImmutableSet
 - Throw UOE for all Map.of().entrySet() mutator methods
 - 8328821: Make the ImmutableCollections clear() call consistent
   
   Without overriding clear(), a call to it in an empty map would
   just return, as iterator.hasNext() would be false. However if
   calling Map.of().clear() throws an exception. To make the
   behavior of Map.of().entrySet().clear() consistent, we need to
   have an implementation of clear() for the entry set that throws
   as well.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18522/files
  - new: https://git.openjdk.org/jdk/pull/18522/files/598af2e5..4c9a511f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18522&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18522&range=02-03

  Stats: 30615 lines in 772 files changed: 17927 ins; 10197 del; 2491 mod
  Patch: https://git.openjdk.org/jdk/pull/18522.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18522/head:pull/18522

PR: https://git.openjdk.org/jdk/pull/18522