[jdk21u-dev] RFR: 8310913: Move ReferencedKeyMap to jdk.internal so it may be shared [v3]

[Aleksey Shipilev]

> Unclean backport to match the codebases between mainline and JDK 21, simplifying maintenance. It also implicitly fixes [JDK-8323505](https://bugs.openjdk.org/browse/JDK-8323505), since this move includes a few touchups to the test.
> 
> The uncleanliness comes from `MethodType.java` conflicts that does not have [JDK-8310849](https://bugs.openjdk.org/browse/JDK-8310849) in JDK 21. So it yields a few contextual conflicts. Since affected hunks are just removals, I removed them by hand.
> 
> There is a follow-up, [JDK-8325255](https://bugs.openjdk.org/browse/JDK-8325255), but it does not seem to affect anything yet, since there are no `ReferenceKeySet.add` calls anywhere in sight. We can backport that separately.
> 
> Additional testing:
>  - [x] MacOS AArch64 Server fastdebug, `jdk/internal/util` tests pass
>  - [x] MacOS AArch64 Server fastdebug, `java/lang/invoke` tests pass
>  - [x] Linux AArch64 Server fastdebug, `all` tests pass

Aleksey Shipilev 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 three additional commits since the last revision:

 - Merge branch 'master' into JDK-8310913-referenced-key-map
 - Merge branch 'master' into JDK-8310913-referenced-key-map
 - Backport 6af0af593446bc33dc94bbf7334c325c4ac0ac0f
   
   Reviewed-by: naoto, rriggs, mchung, liach

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

Changes:
  - all: https://git.openjdk.org/jdk21u-dev/pull/342/files
  - new: https://git.openjdk.org/jdk21u-dev/pull/342/files/62409055..46a84f54

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=342&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=342&range=01-02

  Stats: 14614 lines in 600 files changed: 8578 ins; 3639 del; 2397 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/342.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/342/head:pull/342

PR: https://git.openjdk.org/jdk21u-dev/pull/342