RFR: 8296158: Refactor the verification of CDS region checksum

[Calvin Cheung]

On Sat, 4 Feb 2023 01:22:16 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> 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.

Code refactoring looks good.

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Marked as reviewed by ccheung (Reviewer).

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