Add AVX2 support to IndexOfAnyValues (dotnet#78863)

Author: MihaZupan

src/libraries/System.Memory/tests/Span/IndexOfAnyValues.cs

@@ -394,7 +394,7 @@ static int LastIndexOfAnyExceptReferenceImpl(ReadOnlySpan<char> searchSpace, Rea
         private static class IndexOfAnyValuesTestHelper
         {
             private const int MaxNeedleLength = 10;
-            private const int MaxHaystackLength = 40;
+            private const int MaxHaystackLength = 100;
 
             private static readonly char[] s_randomAsciiChars;
             private static readonly char[] s_randomLatin1Chars;