Fix self inheritance type checks for traits

[iluuu1994]

Fixes GH-18295

[Girgias]

Isn't this also a possible issues for trait constants and properties that declare a type of self.

Also I'm somehow confused why we need to re-iterate and call zend_fixup_trait_method when it should already be called by zend_do_traits_method_binding().

But isn't the problem maybe with fixup_trait_scope() not being called at the appropriate time?

[iluuu1994]

So, what happens:

• self in traits remains self, it is not inferred.
• During inheritance, trait methods are added to the class first. self in types remains, and will be replaced with func->scope at runtime and during inheritance checks.
• This part is new in this PR: Once we're done with adding trait methods, we go through them again to set their scope to the target class. This is done after traits are added so we can distinguish between methods added through traits and those added directly to the class. This distinction matters, because classes may shadow trait methods, but will error when trying to add the same method from multiple traits.
• When linking the parent class, we perform compatibility checks between child and parent methods. Before this PR, self would be incorrectly resolved to the trait instead of the target class, leading to incompatibility errors.
• After linking parent, we go through traits again if they contained any abstract methods. Abstract methods are not actually added to the parent, we will only check whether they are correctly implemented, after all inheritance steps have been performed.
• Because traits suck, there's another exception to this: use T { T::func as func2 }. In this case, not only func but also func2 are methods that need to be implemented. func2 will be copied to the class if it doesn't exist there. We then need to go over these methods again, fix the scope, and more importantly add the ZEND_ACC_IMPLICIT_ABSTRACT_CLASS flag to the class, so that we will actually error due to unimplemented methods.

That said, we can likely move the other zend_fixup_trait_method iteration into the if (trait_contains_abstract_methods) { so that we only perform this repeated iteration when we actually added more functions. I'll try this in a second.