Improve pref of `Array.IndexOf()` for certain `T`. (dotnet/coreclr#24293)

Improve pref of `Array.IndexOf()` for certain `T`. (dotnet/coreclr#24293)

Applies changes to `Array.IndexOf()` and `Array.LastIndexOf()` similar
to the changes made in dotnet/coreclr#20855, so that types other than `byte` and
`char` can use use the fast vectorized path.

Also allows 32-bit and 64-bit types for which
`RuntimeHelpers.IsBitwiseEquatable<T>()` returns `true` to use the
faster implementation of `IndexOf` and `LastIndexOf` from
`MemoryExtensions`.

Commit migrated from https://github.com/dotnet/coreclr/commit/2551753281ce89be4321c3d23111db6c6b7e77c0