Improve SpanHelpers.IndexOfAny(byte,byte)

[benaadams]

The better approached used in #40729

| Faster                                                   | base/diff | Base Median (ns) | Diff Median (ns) | Modality|
| -------------------------------------------------------- | ---------:| ----------------:| ----------------:| --------:|
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 16)   |      1.45 |             5.02 |             3.45 |         |
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 24)   |      1.52 |             5.93 |             3.91 |         |
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 32)   |      1.44 |             6.09 |             4.23 |         |
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 48)   |      1.69 |             5.82 |             3.45 |         |
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 64)   |      1.40 |             5.82 |             4.17 |         |
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 128)  |      1.29 |             6.36 |             4.94 |         |
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 512)  |      1.43 |            10.75 |             7.54 |         |
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 256)  |      1.34 |             7.58 |             5.67 |         |
| System.Memory.Span<Byte>.IndexOfAnyTwoValues(Size: 1024) |      1.11 |            12.99 |            11.69 |         |

Will effect header parsing in Kestrel

length = span.IndexOfAny(ByteCR, ByteLF)

/cc @adamsitnik @danmosemsft

[gfoidl]

Typo.

[danmoseley]

@benaadams @sebastienros is there a way to quantify how much it would help Kestrel? Would help prioritize review.

[benaadams]

Top one of the SpanHelpers for PlainText Platform on Citrine on Linux

Not sure how it changes it though :)

[kunalspathak]

Thanks for doing this for ARM as well.

[kunalspathak]

LGTM. Thanks for doing this.

[jeffhandley]

Beautiful comment; thank you.

[danmoseley]

@sebastienros do you expect this to materially improve Plaintext, given data above?

[sebastienros]

We can hope it doesn't make it slower! Ideally any perf related work should be measured before merged, even more that close to rc. We'll have to look at the charts once the build is available. We can also do a custom with the next build containing this change. I'll follow the CI.

[jeffhandley]

I recommended to @kunalspathak that we go ahead and merge, but good point, @sebastienros. Thanks for checking on it.

[adamsitnik]

@benaadams thank you for another great improvement!

@kunalspathak big thanks for reviewing and merging the PR!