RFR: 8303418: Improve parameter and variable names in BitMap [v2]

[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 incrementally with one additional commit since the last revision:

  copyrights

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12798/files
  - new: https://git.openjdk.org/jdk/pull/12798/files/cccf2fc0..59138b0f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12798&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12798&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 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