Add PHP 8.0+ Union and Intersection type support on SelfValueVisitor

[samsonasik]

Closes #503

[samsonasik]

@lisachenko could you review this? Thank you.

[lisachenko]

PS. The more I look on the SelfValueVisitor/SelfValueTransformer classes - the more I think that they do very strange and incorrect job, which I would like to completely rewrite to enable pretty-printing and to switch to AST-only transformation.

FYI: I'm now in the process of slow refactoring of entire AST/transformation subsystem, so expect significant changes in this part soon )

Could you please check if current PR works with the latest master branch or not (try to rebase and check locally please)? I've some bad feeling that there is a regression issue from my recent refactoring of goaop/parser-reflection that renders 'self' now with '\self' (

[samsonasik]

Using dev-master seems working ok

[samsonasik]

@lisachenko Ready to merge 👍

[samsonasik]

@lisachenko Ready to merge 👍

[samsonasik]

Also handled self usage in anonymous class

[samsonasik]

@lisachenko Ready to merge 👍

[lisachenko]

Squashed and merged into the main branch. Thanks!