<i18n dev> RFR: 8302871: Speed up StringLatin1.regionMatchesCI [v10]

[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 two additional commits since the last revision:

 - Replace 'oldest ASCII trick in the book' use in toUpperCase, toLowerCase with "by removing (setting) a single bit"
 - Align local variable naming in toLowerCase, toUpperCase with equalsIgnoreCase by using 'lower' and 'upper'

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12632/files
  - new: https://git.openjdk.org/jdk/pull/12632/files/6588ab0f..44d91544

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12632&range=09
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12632&range=08-09

  Stats: 11 lines in 1 file changed: 2 ins; 0 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