[9.x] Add option to ignore case in Str::contains and Str::containsAll

[ksassnowski]

This PR adds a third parameter $ignoreCase to Str::contains and Str::containsAll to allow for case-insensitive comparisons.

Motivation

I often find myself doing something like this in my code

Str::contains(Str::lower($user->first_name), Str::lower($request->query('q'));

This gets especially annoying when trying to compare against multiple fields

$normalizedQuery = Str::lower($request->query('q'));

$matches = Str::contains(Str::lower($user->first_name), $normalizedQuery) 
          || Str::contains(Str::lower($user->last_name), $normalizedQuery);

Changes

With this PR, it would be possible to do this instead:

Str::contains($user->first_name, $request->query('q'), true);

I added the same parameter to Str::containsAll. To avoid doing the transformation inside a loop, it gets applied only once inside containsAll before calling static::contains.

The $ignoreCase parameter is false by default so the existing behavior doesn’t change.