Vectorize the new {Last}IndexOfAnyExcept methods

[stephentoub]

Simple implementations were added in #67941. These should be vectorized, ideally sharing as much implementation as possible with {Last}IndexOf{Any}.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[EgorBo]

Can help anyone who decides to try it

[stephentoub]

@GrabYourPitchforks suggested we could possibly share the bulk of the IndexOf{Any} implementations, using a generic type parameter ala

runtime/src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.cs

Lines 206 to 209 in 4017327

	private unsafe void ChangeCaseCommon<TConversion>(ref char source, ref char destination, int charCount) where TConversion : struct
	{
	Debug.Assert(typeof(TConversion) == typeof(ToUpperConversion) || typeof(TConversion) == typeof(ToLowerConversion));
	bool toUpper = typeof(TConversion) == typeof(ToUpperConversion); // JIT will treat this as a constant in release builds

to control whether we're including or excluding the specified values.

But I expect we should wait to attempt that until it's been converted over to Vector128/256 (#64451), so maybe we should put something simple in place, maybe just for 1-3 chars, maybe just a single vectorized path (with Vector<T> or Vector128<T>) until the IndexOf{Any} code has stabilized.

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Issue Details

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Simple implementations were added in #67941. These should be vectorized, ideally sharing as much implementation as possible with {Last}IndexOf{Any}.

Author:	stephentoub
Assignees:	-
Labels:	area-System.Memory, tenet-performance, up-for-grabs
Milestone:	7.0.0