RFR: 8304016: Add BitMap find_last suite of functions [v3]

[Kim Barrett]

> Please review this change that adds functions to BitMap for finding the last
> set/clear bit in a range.
> 
> Testing:
> mach5 tier1, including new gtesting for the new functions.

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 four additional commits since the last revision:

 - Merge branch 'master' into find-last
 - shrink find_first_bit_impl
 - improve find_last_bit_impl
 - find_last_set/clear_bit

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12988/files
  - new: https://git.openjdk.org/jdk/pull/12988/files/b3d2aed1..fcfebb2a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12988&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12988&range=01-02

  Stats: 78648 lines in 898 files changed: 48978 ins; 20413 del; 9257 mod
  Patch: https://git.openjdk.org/jdk/pull/12988.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12988/head:pull/12988

PR: https://git.openjdk.org/jdk/pull/12988