Add combination operators to selectors

[gplanchat]

Following #186

[sonarqubecloud]

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29.3% Duplication

[carlosas]

Hey! Thank you a lot for the PR!

I had this feature in mind for a long time. Actually the current refactor to phpstan extension that I'm working on it's partially prepared for it https://github.com/carlosas/phpat/tree/phpstan/src/Selector/Modifier

I will review it ASAP in the following days

[gplanchat]

Hello @carlosas,

I checked the phpstan branch and tried to implement it on this branch. I could not make the tests work.

[carlosas]

I just saw that the last version of PHPStan has changed some signatures, and my fake implementations of some dependencies got broken. I have disabled the unit tests for now and will work on testing properly.

If you want, you could drop a draft PR against the branch v0.10x and we can check manually if the approach works. Then I can help you polishing the feature and tests :)

Take into account that in v0.10 the method ->classes() accepts multiple Selectors and behaves as an OR (see the Test definition section in the new README)
Also I would like to discuss the name of the methods.

I'll close this PR for now. Do you mind opening a new one with the draft phpstan approach?
Thanks a lot!