Extend case optimization in MatchCharacterClass to all chars that differ by one bit

[stephentoub]

In RegexCompiler / source generator, we optimize matching a set like [Aa] to just do (ch | 0x20) == 'a'. But we can trivially extend this to any pair of characters that differ by only a single bit and not just to casing.

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Issue Details

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In RegexCompiler / source generator, we optimize matching a set like [Aa] to just do (ch | 0x20) == 'a'. But we can trivially extend this to any pair of characters that differ by only a single bit and not just to casing.

Author:	stephentoub
Assignees:	-
Labels:	area-System.Text.RegularExpressions, tenet-performance
Milestone:	-

[joperezr]

LGTM. Can we add a couple of tests that use this which are not just casing?

[stephentoub]

Can we add a couple of tests that use this which are not just casing?

We have some (I know because I had a bug that caused a variety of tests to fail), but I can add some explicitly.