FIX Allow passing objects to InjectionCreator::create()

[emteknetnz]

Issue #10533

Replacement for #10539

Main difference is the use of get_class($class) instead of return $class to ensure that a new instance is always created. I've also changed the unit testing.

I've also tidied up some of the previous ?? '' added as part of the php 8.1 code-writing

This is technically a bugfix since it restores previous behavior of allow anonymous classes, which will unintentional, seems like it has a valid use case in unit testing. Anonymous classes can be cleaner to use then the at times cumbersome combination of TestOnly classes with private static $extra_dataobjects

I've put n8-dev down as a co-author

[michalkleiner]

Looks good to me!

[emteknetnz]

@n8-dev I've tagged 4.11.11 for you https://github.com/silverstripe/silverstripe-framework/releases/tag/4.11.11