Use ReadOnlySpan<char> equivalents for string methods?

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In #39743 I found that there were performance gains available from using someString.AsSpan().IndexOfAny(...) in the code instead of someString.IndexOfAny(...).

This raises the possibility that there are other usages of string-based operations that could potentially receive a performance boost from using equivalent operations available for spans in the MemoryExtensions class (though the original motivation was to remove the static char arrays).

To pick a specific example, IndexOf(ReadOnlySpan<char> value, StringComparison comparisonType) could be used here if AsSpan() were added:

https://github.com/dotnet/aspnetcore/blob/570bf070e95a2bc559a4b616240574dee954232c/src/Http/Http/src/BindingAddress.cs#L130

Assuming a positive improvement of a large enough magnitude (open question: how big would that be?) is available from benchmarking candidate cases (which also raises the possibility of a runtime analyzer to find such candidates in the first place?), would a larger scale adoption of this pattern (and the subsequent sprinkling of AsSpan() through the code base) be welcomed in ASP.NET Core?

If so, I'd be happy to help out with evaluating/adopting them as determined by such an exercise.

This seems to be the sort of thing where lots of small changes could add up to nice overall benefit, but comes with the potential code style issue of doing so, and the maintenance overhead of continuing to use such a pattern in the code over time.

Describe the solution you'd like

1. Benchmark candidate call sites of string method usage that have ReadOnlySpan<T> equivalents available for each project file's target frameworks.
2. Update worthy candidate call sites (determined by meeting a TBD threshold of improvement) to add AsSpan() (By area? Splitting it up would prevent a giant PR summoning lots of Code Owners for review, for example).
3. Observe net result on ASP.NET Core benchmarks once all agreed candidates updated.

Additional context

No response