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

[Liam Miller-Cushon]

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

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Commit messages:
 - Use AbstractImmutableSet
 - Throw UOE for all Map.of().entrySet() mutator methods
 - 8328821: Make the ImmutableCollections clear() call consistent

Changes: https://git.openjdk.org/jdk/pull/18522/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18522&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328821
  Stats: 36 lines in 2 files changed: 35 ins; 0 del; 1 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