feat: add language feature for php8.0, add strong types, adjust tests

[Chris53897]

Hi, this PR addresses the following points.

• add language feature for php8.0
• add strong types
• adjust tests
• Remove some tests for types that in my eyes are not needed anymore.
• Fix some tests (see static::getContainer() )

Questions:

• isValidForSearch($value) Parameter mixed vs string? I changed it to mixed
• Different return types of configureOptions() void vs OptionsResolver What is the desired behaviour? Should be consistent in my point of view.

There is still one Test not working with symfony6 ORMAdapterEventsTest->testPreQueryEvent() but that should be fixed in an other PR

[curry684]

I fixed most of this with major maintenance already, except the strong types. The PR should be mergeable still if you rebase I think.

[Chris53897]

@curry684 Thanks for having a look and maintenance. I will have a look at your changes.

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