Fixesdotnet/runtime#78587

Flags 3 cases in dotnet/runtime, all of them in projects where we've avoided making the switch because they multi-target to older TFMs (SearchValues is a .NET 8+ API).

The analyzer flags cases like

conststringMyValues="abcdef";readonlychar[]MyValues=new[]{'a','b','c','d','e','f'};span.IndexOfAny("abcdef");span.IndexOfAny("abcdef"u8);span.IndexOfAny(MyValues);span.IndexOfAny(new[]{'a','b','c','d','e','f'});string.IndexOfAny("abc".ToCharArray());

for all{Last}IndexOfAny{Except} andContainsAny{Except} overloads forbyte/char and suggests that they be rewritten as

privatestaticreadonlySearchValues<char>s_myChars=SearchValues.Create("abcdef");span.IndexOfAny(s_myChars);

We'll also rewrite thestring.IndexOfAny(char[]) overload to usestring.AsSpan().IndexOfAny(SearchValues) instead.
We won't do the same forIndexOfAny(char[], int) orIndexOfAny(char[], int, int) as they would require us to inject more logic to account for the differences in behavior (returning offset from start vs. from 0)

If the values are specified by a constant in an appropriate scope, we'll reuse said constant to feed theSearchValues.Create.

If we're not using the original member and there are now no other uses, we'll remove it.

For a full list of patterns that we do/don't recognize, seethis test source.

Potential improvements:

• IDE0300 will suggest replacingnew[] { 'a', 'b', 'c' } with['a', 'b', 'c'], whereas this analyzer does not recognize collection literals.