Simplify IndexOfAnyAsciiByteValues for needles with 0 on X86

[MihaZupan]

IndexOfAnyLookupCore already discards non-ASCII byte values.
We have to do this special-casing of 0 for char inputs because of how we pack the source on X86, but it's redundant when dealing with byte inputs where we do no such packing.

@stephentoub this will further improve your change in #82789 that hits this case.
For values that contain 0:

Method	Toolchain	Length	Mean	Error	Ratio
IndexOfAny_Byte	main	1000	36.95 ns	0.127 ns	1.00
IndexOfAny_Byte	pr	1000	30.12 ns	0.048 ns	0.81
IndexOfAnyExcept_Byte	main	1000	39.75 ns	0.134 ns	1.00
IndexOfAnyExcept_Byte	pr	1000	32.48 ns	0.054 ns	0.82
LastIndexOfAny_Byte	main	1000	37.09 ns	0.088 ns	1.00
LastIndexOfAny_Byte	pr	1000	30.42 ns	0.062 ns	0.82
LastIndexOfAnyExcept_Byte	main	1000	39.67 ns	0.127 ns	1.00
LastIndexOfAnyExcept_Byte	pr	1000	31.98 ns	0.269 ns	0.81

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Issue Details

---

IndexOfAnyLookupCore already discards non-ASCII byte values.
We have to do this special-casing of 0 for char inputs because of how we pack the source on X86, but it's redundant when dealing with byte inputs where we do no such packing.

@stephentoub this will further improve your change in #82789 that hits this case.
For values that contain 0:

Method	Toolchain	Length	Mean	Error	Ratio
IndexOfAny_Byte	main	1000	36.95 ns	0.127 ns	1.00
IndexOfAny_Byte	pr	1000	30.12 ns	0.048 ns	0.81
IndexOfAnyExcept_Byte	main	1000	39.75 ns	0.134 ns	1.00
IndexOfAnyExcept_Byte	pr	1000	32.48 ns	0.054 ns	0.82
LastIndexOfAny_Byte	main	1000	37.09 ns	0.088 ns	1.00
LastIndexOfAny_Byte	pr	1000	30.42 ns	0.062 ns	0.82
LastIndexOfAnyExcept_Byte	main	1000	39.67 ns	0.127 ns	1.00
LastIndexOfAnyExcept_Byte	pr	1000	31.98 ns	0.269 ns	0.81

Author:	MihaZupan
Assignees:	MihaZupan
Labels:	area-System.Memory
Milestone:	8.0.0

[stephentoub]

Nice

[MihaZupan]

/azp run runtime-libraries-coreclr outerloop

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