RFR: 8302871: Speed up StringLatin1.regionMatchesCI [v12]

[Eirik Bjorsnos]

On Wed, 22 Feb 2023 16:37:45 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> 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:
> 
>   Make the loop variables chars to avoid casting

Thanks for reviews Claes and Martin! I'll let this linger a bit before integrating in case Alan has comments after the latest updates.

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