<i18n dev> RFR: 8302871: Speed up StringLatin1.regionMatchesCI [v3]

[Eirik Bjorsnos]

> This PR suggests we can speed up `StringLatin1.regionMatchesCI` by applying 'the oldest ASCII trick in the book'.
> 
> The new static method `CharacterDataLatin1.equalsIgnoreCase` compares two latin1 bytes for equality ignoring case. `StringLatin1.regionMatchesCI` is updated to use `equalsIgnoreCase`
> 
> To verify the correctness of `equalsIgnoreCase`, a new test is added  to `EqualsIgnoreCase` with an exhaustive verification that all 256x256 latin1 code point pairs have an `equalsIgnoreCase` consistent with Character.toUpperCase, Character.toLowerCase.
> 
> Performance is tested for matching and mismatching cases of code point pairs picked from the ASCII letter, ASCII number and latin1 letter ranges. Results in the first comment below.

Eirik Bjorsnos has updated the pull request incrementally with one additional commit since the last revision:

  Add clarifying comments and use more descriptive variable names in the latin1 verification EqualsIgnoreCase test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12632/files
  - new: https://git.openjdk.org/jdk/pull/12632/files/59c42298..84517102

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12632&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12632&range=01-02

  Stats: 16 lines in 1 file changed: 5 ins; 2 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/12632.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12632/head:pull/12632

PR: https://git.openjdk.org/jdk/pull/12632