RFR: 8296158: Refactor the verification of CDS region checksum [v3]

[Ioi Lam]

> Consolidate the two old functions
> 
> - `FileMapInfo::region_crc_check(char* buf, size_t size, int expected_crc)`
> - `FileMapInfo::verify_region_checksum(int i)`
> 
> Into a single function `FileMapRegion::check_region_crc()`.
> 
> Also performed some minor renaming and removed a useless API.

Ioi Lam 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 three additional commits since the last revision:

 - Merge branch 'master' into 8296158-refactor-cds-region-crc-check
 - @matias9927 suggestions
 - 8296158: Refactor the verification of CDS region checksum

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12424/files
  - new: https://git.openjdk.org/jdk/pull/12424/files/10dcd0b1..52a5f4be

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12424&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12424&range=01-02

  Stats: 56650 lines in 1287 files changed: 24572 ins; 15545 del; 16533 mod
  Patch: https://git.openjdk.org/jdk/pull/12424.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12424/head:pull/12424

PR: https://git.openjdk.org/jdk/pull/12424