Use SearchValues<string> in Regex

[stephentoub]

Once SearchValues.Create(ReadOnlySpan<string>, StringComparison) is available, we can use it in Regex to accelerate the search for patterns that begin with alternations, sets, etc.

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Issue Details

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Once IndexOfAnyValues.Create(ReadOnlySpan<string>, StringComparison) is available, we can use it in Regex to accelerate the search for patterns that begin with alternations, sets, etc.

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-System.Text.RegularExpressions
Milestone:	8.0.0

[stephentoub]

SearchValues<string> is being used now by regex for case-insensitive. We can opportunistically add in use for case-sensitive as we find worthwhile cases for it.