Rework ProbabilisticMap character checks in SearchValues

[MihaZupan]

Contributes to #100315 (comment)

The probabilistic map uses an O(i * m) fallback for -Except methods (scan all the values for each character in the input).
We use the same O(m) helper (scan the values) to confirm potential matches in the vectorized helper.

This PR adds support for the probmap to use an O(1) contains check for -Except methods and match confirmations.
The check is effectively a perfect hash check entries[value % entries.Length] == value, but implemented using a variant of FastMod. These checks can be inlined into the vectorized methods while not consuming too much memory.
We use this only when the probmap is computed as part of SearchValues as finding an optimal modulus is relatively expensive (see ProbabilisticMapState.FindModulus - there are probably smarter ways to go about it). When the probabilistic map is created for single-use IndexOfAny operations, we still use the same O(m) checks as before.

This PR also replaces the Latin1CharSearchValues implementation with BitmapCharSearchValues, which can use a bitmap of arbitrary size (not limited to [0, 255]). We use this when we guess that it'll be faster than the ProbabilisticMap (e.g. there are a lot of values in the set, or the set is dense and the probmap isn't vectorized).
I haven't changed the condition when we use ProbabilisticWithAsciiCharSearchValues as there are plausible cases where the ASCII fast path may still be useful even if the probabilistic path could be a bitmap instead.

Improvements for early matches (cheaper confirmation step)

public class IndexOfAnyMixedAsciiNonAscii
{
    private static readonly SearchValues<char> s_charsWithNonAscii = SearchValues.Create("-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzK");
    private const string Text = "űaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";

    [Benchmark] // This one will do the confirmation inside the vectorized path
    public int IndexOfAny() => Text.AsSpan().IndexOfAny(s_charsWithNonAscii);
}

Method	Toolchain	Mean	Error	Ratio
IndexOfAny	main	11.236 ns	0.0375 ns	1.00
IndexOfAny	pr	7.768 ns	0.0412 ns	0.69

Improvements for IndexOfAnyExcept (O(1) instead of O(m) character checks)

public class IndexOfAnyMixedAsciiNonAscii
{
    private static readonly SearchValues<char> s_charsWithNonAscii = SearchValues.Create("-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzK");
    private static readonly string _textExcept = new string('K', 1000);

    [Benchmark]
    public int IndexOfAnyExcept() => _textExcept.AsSpan().IndexOfAnyExcept(s_charsWithNonAscii);
}

Method	Toolchain	Mean	Error	Ratio
IndexOfAnyExcept	main	2,832.7 ns	10.65 ns	1.00
IndexOfAnyExcept	pr	675.2 ns	2.39 ns	0.24

Speedup factor is going to depend on how many values are in the set and how early in the values each input character matched with the previous implementation.
With the new implementation, the throughput is less dependent on the haystack.

The bitmap vs probmap hash O(1) checks

public class IndexOfAnyMixedAsciiNonAscii
{
    private static readonly SearchValues<char> s_bitmap = SearchValues.Create(new string('\u0080', 256) + '\u0082');
    private static readonly SearchValues<char> s_probmap = SearchValues.Create(new string('\u0080', 100) + '\uF000');
    private static readonly string TextExcept = new string('\u0080', 1000);

    [Benchmark]
    public int Bitmap() => TextExcept.AsSpan().IndexOfAnyExcept(s_bitmap);

    [Benchmark]
    public int Probmap() => TextExcept.AsSpan().IndexOfAnyExcept(s_probmap);
}

Method	Mean	Error
Bitmap	754.2 ns	14.42 ns
Probmap	868.3 ns	0.11 ns

This happens to bring all SearchValues<char> implementations to an O(i) worst-case (from O(i * m)).

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-buffers
See info in area-owners.md if you want to be subscribed.

[danmoseley]

Are all these well covered in the perf repo?

[MihaZupan]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[MihaZupan]

Are all these well covered in the perf repo?

Yes, mainly by the ßäöüÄÖÜ values.
The BitmapCharSearchValues would be covered by platforms without explicit ISA support.

Results

Method	Toolchain	Values	Mean	Error	Ratio
Contains	main	ßäöüÄÖÜ	1.832 ns	0.0125 ns	1.00
Contains	pr	ßäöüÄÖÜ	1.734 ns	0.0058 ns	0.95
ContainsAny	main	ßäöüÄÖÜ	21.025 ns	1.5866 ns	1.01
ContainsAny	pr	ßäöüÄÖÜ	15.148 ns	0.1088 ns	0.73
IndexOfAny	main	ßäöüÄÖÜ	21.404 ns	2.7379 ns	1.03
IndexOfAny	pr	ßäöüÄÖÜ	15.867 ns	0.5050 ns	0.76
LastIndexOfAny	main	ßäöüÄÖÜ	124.294 ns	0.1215 ns	1.00
LastIndexOfAny	pr	ßäöüÄÖÜ	91.647 ns	0.1313 ns	0.74
LastIndexOfAnyExcept	main	ßäöüÄÖÜ	270.352 ns	0.0708 ns	1.00
LastIndexOfAnyExcept	pr	ßäöüÄÖÜ	91.775 ns	0.0788 ns	0.34
IndexOfAnyExcept	main	ßäöüÄÖÜ	273.921 ns	0.7002 ns	1.00
IndexOfAnyExcept	pr	ßäöüÄÖÜ	76.792 ns	0.3625 ns	0.28

[EgorBo]

Improvements on arm64: dotnet/perf-autofiling-issues#34817