RFR: 8309622: Re-examine the cache mechanism in BaseLocale [v6]

[Naoto Sato]

> This is stemming from the PR: https://github.com/openjdk/jdk/pull/14211 where aggressive GC can cause NPE in `BaseLocale$Key` class. I refactored the in-house cache with WeakHashMap, and removed the Key class as it is no longer needed (thus the original NPE will no longer be possible). Also with the new JMH test case, it gains some performance improvement:
> 
> (w/o fix)
> 
> Benchmark                       Mode  Cnt      Score     Error  Units
> LocaleCache.testForLanguageTag  avgt   20   5781.275 ± 569.580  ns/op
> LocaleCache.testLocaleOf        avgt   20  62564.079 ± 406.697  ns/op
> 
> (w/ fix)
> Benchmark                       Mode  Cnt      Score     Error  Units
> LocaleCache.testForLanguageTag  avgt   20   4801.175 ± 371.830  ns/op
> LocaleCache.testLocaleOf        avgt   20  60394.652 ± 352.471  ns/op

Naoto Sato has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 31 commits:

 - Restored the test
 - Merge branch 'master' into JDK-8309622-Cache-BaseLocale
 - Merge branch 'master' of https://git.openjdk.org/jdk into JDK-8309622-Cache-BaseLocale
 - small cleanup
 - Merge branch 'pull/14684' into JDK-8309622-Cache-BaseLocale
 - Update ReferencedKeyTest.java
 - Simple versions of create
 - Add flag for reference queue type
 - Merge branch 'master' into 8310913
 - Update to use VirtualThread friendly stale queue.
 - ... and 21 more: https://git.openjdk.org/jdk/compare/99ea8bf2...b1f64e93

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Changes: https://git.openjdk.org/jdk/pull/14404/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14404&range=05
  Stats: 522 lines in 6 files changed: 129 ins; 266 del; 127 mod
  Patch: https://git.openjdk.org/jdk/pull/14404.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14404/head:pull/14404

PR: https://git.openjdk.org/jdk/pull/14404