RFR: 8303418: Improve parameter and variable names in BitMap [v3]

[Kim Barrett]

> Please review this change to names in BitMap.
> 
> - Parameters that designate a bit in a BitMap are named "bit".
> - Parameters that designate a word in the underlying BitMap storage are named "word".
> - Parameters that designate a range are named "beg" and "end" resp.
> 
> Added helper function `flipped_word` for use by `get_next_bit_impl`, replacing
> the odd overload for `map`.
> 
> In `get_next_bit_impl`, prefixed the variables "index" and "limit" with
> "word_" to make clear the units.
> 
> Testing:
> mach5 tier1

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 improve-bitmap-varnames
 - copyrights
 - improve names in get_next_bit_impl
 - cleanup parameter names

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12798/files
  - new: https://git.openjdk.org/jdk/pull/12798/files/59138b0f..cb665e54

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12798&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12798&range=01-02

  Stats: 3035 lines in 106 files changed: 2058 ins; 624 del; 353 mod
  Patch: https://git.openjdk.org/jdk/pull/12798.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12798/head:pull/12798

PR: https://git.openjdk.org/jdk/pull/12798