RFR: 8316493: Remove the caching fields in AbstractMap [v11]

[Per Minborg]

> This PR outlines a solution for making immutable maps `@ValueBased` by removing cacheing of certain values in `AbstractMap`.
> 
> By removing these caching fields in `AbstractMap`, we can make the immutable maps `@ValueBased` and at the same time, performance is likely improved because the JVM is probably able to optimize away object creation anyway via escape analysis. Also, all maps will occupy less space as we get rid of a number of objects and references stored for each map.
> 
> We need to benchmark this solution to better understand its implications.

Per Minborg has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 14 commits:

 - Merge branch 'master' into vb-map2
 - Fix formatting
 - Remove caching in TreeMap
 - Remove caching from CHM and CSLM
 - Move back clone to original position
 - Reintroduce AbstractMap::clone
 - Add 'fresh' to implSpec
 - Remove AbstractMap::clone
 - Merge master
 - Merge branch 'master' into vb-map2
 - ... and 4 more: https://git.openjdk.org/jdk/compare/9cce9fe0...b1bfcd17

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Changes: https://git.openjdk.org/jdk/pull/15614/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15614&range=10
  Stats: 295 lines in 11 files changed: 92 ins; 165 del; 38 mod
  Patch: https://git.openjdk.org/jdk/pull/15614.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15614/head:pull/15614

PR: https://git.openjdk.org/jdk/pull/15614