Add support for printing Enums when using PHP 8.1

[gabrielanhaia]

Change Log

Added

- Support for printing Enums when using PHP 8.1

Fixed

Changed

Now it's possible to print Enums, however We will need a new version (probably) for backward compatibility.

Removed

Deprecated

Security

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Description

• It was implemented the possibility to print Enums when using PHP8.1+
• I changed the minimum version of PHP to 8.1 in the composer.json file, probably We will need a 4.x version or something like that to keep the previous versions working.
• If you take a look at my PR you will see that the return of \gettype in the case of an Enum is still an object for PHP. That is why I had to combine the \get_class and this new nice PHP function enum_exists

[gabrielanhaia]

@norberttech Proposition of an improvement now that PHP 8.1 is out there

[norberttech]

Do we really need to break BC to support enums? It might be better to probably just check if method enum_exists and then use it to check if given value is an enum and use it.
Could you also add 8.1 to testsuite matrix in github action workflow files?