[11.x] Allow using strings when controlling UUID generation

[timacdonald]

This PR allows improves the use of strings when controlling UUIDs in your testsuite. A Uuid object is now always returned.

Str::uuid(); // instanceof Uuid
Str::uuid()->toString(); // is_string

Str::createUuidsUsingSequence(['6201c046-a8d7-47e5-8ac7-cd0cbdb3b9f4']);

// Before...

Str::uuid(); // '6201c046-a8d7-47e5-8ac7-cd0cbdb3b9f4'

// Now...

Str::uuid(); // instanceof Uuid
Str::uuid()->toString(); // '6201c046-a8d7-47e5-8ac7-cd0cbdb3b9f4'

This also applies to the more generic createUuidsUsing:

Str::uuid(); // instanceof Uuid
Str::uuid()->toString(); // is_string


Str::createUuidsUsing(fn () => '6201c046-a8d7-47e5-8ac7-cd0cbdb3b9f4');

// Before...

Str::uuid(); // '6201c046-a8d7-47e5-8ac7-cd0cbdb3b9f4'

// Now...

Str::uuid(); // instanceof Uuid
Str::uuid()->toString(); // '6201c046-a8d7-47e5-8ac7-cd0cbdb3b9f4'

[Jubeki]

Hey @timacdonald, I think you should add a check for using a null value. Because that would be unsetting the factoring normally, but now be called as a function.

[taylorotwell]

Tests failing on this one.