Handle FuncCall nodes that represent first class callables

[spawnia]

Stumbled upon this while working on a fix for #31. The original fix no longer applies, but I think this is still valuable to ensure PHP 8.1 compatibility.

[dbrekelmans]

@spawnia Could you resolve the conflict?

Also would this interact with #33? I'm thinking it might be best to merge this PR before #33, what do you think?

[spawnia]

@dbrekelmans I rebased atop the latest changes. I think #33 and this can be applied independently from one another. The condition I put to check for first class callables should come before the condition added there.

[shish]

Hi all, new maintainer here, hoping to get this merged if it's still relevant. Coming in with little context, what does the PR do? Could it include a unit test showing what fails now, and succeeds after the patch is applied?

(There are merge conflicts and failing tests, and I daren't try to fix it myself without understanding the intention behind the code 😅 )

[spawnia]

Thank you @shish for looking into this. I tried adding a failing test. I think first-class callables should also be recognized by this rule, such as json_encode(...).

[shish]

I have enabled the CI, but it looks like the added unit test is failing both before and after the changes to add support for it o.o;;

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.54%. Comparing base (4e0c969) to head (9d145a4).
Report is 3 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #32      +/-   ##
============================================
+ Coverage     92.70%   94.54%   +1.83%     
- Complexity       40       46       +6     
============================================
  Files             7        8       +1     
  Lines            96      110      +14     
============================================
+ Hits             89      104      +15     
+ Misses            7        6       -1     

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[spawnia]

Looks like PHPStan has introduced a custom node type for first-class callables from functions, see https://apiref.phpstan.org/2.1.x/PHPStan.Node.FunctionCallableNode.html.

[spawnia]

@shish I hope you don't mind the restructuring of the tests. I found it hard to fit in the new tests in a logical and structured manner without it.