RFR: 8307926: Support byte-sized atomic bitset operations [v2]

[Kim Barrett]

> Please review this change to add support Atomic byte-sized bitset operations.
> The existing default implementation using cmpxchg already (by accident) works
> on such values, because cmpxchg supports byte-sized operations.  Any future
> platform specializations of these operations will need to deal with this size
> too.
> 
> The changes consist of updating the requirements documentation for the
> operations and adding gtests for the newly supported size.
> 
> Testing:
> mach5 tier1-3
> GHA testing

Kim Barrett 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 two additional commits since the last revision:

 - Merge branch 'master' into atomic-bitops-bytes
 - support bitops on bytes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13952/files
  - new: https://git.openjdk.org/jdk/pull/13952/files/3ef97e7d..cf5084b4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13952&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13952&range=00-01

  Stats: 4297 lines in 175 files changed: 2814 ins; 420 del; 1063 mod
  Patch: https://git.openjdk.org/jdk/pull/13952.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13952/head:pull/13952

PR: https://git.openjdk.org/jdk/pull/13952