RFR: 8296785: Use realloc for CHeap-allocated BitMaps [v3]

[Stefan Karlsson]

> Today CHeap allocated bitmaps don't resize with realloc. I'd like to change that by fixing that by adding support for realloc in the ArrayAllocator classes, and then use that when resizing the bitmaps.
> 
> We've been using and testing one version of this patch in the Generational ZGC repository for a while now. That version is slightly different because of recent rewrites of the bitmaps, but in essence the same. See:
> https://github.com/openjdk/zgc/commit/ca692f686bda8d86d3786c2afc782bfdc54fbdfc

Stefan Karlsson has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Fixes after merge
 - Merge remote-tracking branch 'upstream/master' into 8296785_bitmap_realloc
 - 8296785: Use realloc for CHeap-allocated BitMaps
 - Merge remote-tracking branch 'upstream/master' into 8296774_bitmap_stricter_construction
 - 8296774: Removed default MEMFLAGS value from CHeapBitMap

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Changes: https://git.openjdk.org/jdk/pull/11102/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11102&range=02
  Stats: 226 lines in 5 files changed: 174 ins; 30 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/11102.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11102/head:pull/11102

PR: https://git.openjdk.org/jdk/pull/11102