Fix comparison with get_class() in traits always evaluate to true

[staabm]

closes phpstan/phpstan#3633

see https://3v4l.org/LalXd

test fails without the src change:

1) PHPStan\Rules\Comparison\StrictComparisonOfDifferentTypesRuleTest::testBug3633
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'23: Strict comparison using === between class-string<Bug3633\HelloWorld> and 'Bug3633\\OtherClass' will always evaluate to false.
+'10: Strict comparison using === between class-string<Bug3633\HelloWorld> and 'Bug3633\\OtherClass' will always evaluate to false.
+23: Strict comparison using === between class-string<Bug3633\HelloWorld> and 'Bug3633\\OtherClass' will always evaluate to false.
+07: Strict comparison using === between class-string<Bug3633\OtherClass> and 'Bug3633\\HelloWorld' will always evaluate to false.
 35: Strict comparison using === between class-string<Bug3633\OtherClass> and 'Bug3633\\HelloWorld' will always evaluate to false.
+07: Strict comparison using === between class-string<Bug3633\FinalClass> and 'Bug3633\\HelloWorld' will always evaluate to false.
+10: Strict comparison using === between class-string<Bug3633\FinalClass> and 'Bug3633\\OtherClass' will always evaluate to false.
 50: Strict comparison using === between class-string<Bug3633\FinalClass> and 'Bug3633\\HelloWorld' will always evaluate to false.
 53: Strict comparison using === between class-string<Bug3633\FinalClass> and 'Bug3633\\OtherClass' will always evaluate to false.
 59: Strict comparison using === between 'Bug3633\\FinalClass' and 'Bug3633\\FinalClass' will always evaluate to true.
 '

[phpstan-bot]

This pull request has been marked as ready for review.

[ondrejmirtes]

We can at least say that it's going to be ClassStringType.

[ondrejmirtes]

Oh, I just realized this PR is more wrong than right.

1. We need to cover the same scenario for get_class() without arguments.
2. We can still return correct specific result for an argument that isn't $this.

[ondrejmirtes]

Thank you.