RFR: JDK-8310913 Move ReferencedKeyMap to jdk.internal so it may be shared [v9]

[Jim Laskey]

> java.lang.runtime.ReferencedKeyMap was introduced to provide a concurrent caching scheme for Carrier objects. The technique used is generally useful for a variety of caching schemes and is being moved to be shared in other parts of the jdk. The MethodType interning case is one example.

Jim Laskey has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 15 commits:

 - Merge branch 'master' into 8310913
 - Requested changes.
   
   Added intern with UnaryOperator<T> interning function to prepare key before adding to set.
 - Update test to check for gc.
 - 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.
 - Remove warning tied to String Templates
 - unneeded SuppressWarning
 - ... and 5 more: https://git.openjdk.org/jdk/compare/028068a6...fbb78778

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Changes: https://git.openjdk.org/jdk/pull/14684/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14684&range=08
  Stats: 1520 lines in 13 files changed: 887 ins; 625 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/14684.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14684/head:pull/14684

PR: https://git.openjdk.org/jdk/pull/14684