RFR: 8316929: Shenandoah: Shenandoah degenerated GC and full GC need to cleanup old OopMapCache entries [v2]

[Zhengyu Gu]

> During STW root scan, interpreted frame's oop map may be cached. But due to limited cache size (32 entries per instance class), entries may be evicted to old entries list due to collision, should be cleanup in VM_Operation's doit_epilogue(), or risk leaking memory.
> 
> Test:
>   hotspot_gc_shenandoah (fastdebug and release on MacOSX)

Zhengyu Gu 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-8316929
 - cleanup
 - 8316929: Shenandoah: Shenandoah degenerated GC and full GC need to cleanup old OopMapCache entries

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15921/files
  - new: https://git.openjdk.org/jdk/pull/15921/files/92dc4f4e..b84d2cad

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15921&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15921&range=00-01

  Stats: 7940 lines in 283 files changed: 5780 ins; 1041 del; 1119 mod
  Patch: https://git.openjdk.org/jdk/pull/15921.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15921/head:pull/15921

PR: https://git.openjdk.org/jdk/pull/15921