Add Span.IndexOfAny overload

[ahsonkhan]

Span.IndexOfAny(Span<byte> span, byte value)

@davidfowl, should the signature take a Span value instead, i.e.
Span.IndexOfAny(Span<byte> span, Span<byte> values)?

Note, we don't need index/count as initially requested:
Span.IndexOfAny(Span<byte> span, byte value, int index, int count)

[benaadams]

should the signature take a Span value instead

Its introducing an unnecessary for loop into the implementation to be general case; would be better to use Span<byte> values as a params type overload; so:

Span.IndexOf(Span<byte> span, byte value)
Span.IndexOfAny(Span<byte> span, byte value1, byte value2)
Span.IndexOfAny(Span<byte> span, byte value1, byte value2, byte value3)
Span.IndexOfAny(Span<byte> span, Span<byte> values)

[ahsonkhan]

Fixed in dotnet/corefx#17357