Relax final+private warning for trait methods with inherited final

[iluuu1994]

Fixes GH-17214

Small note: I thought we'd have to support as final private, which would not work with this approach. But then noticed that strangely the grammar only allows for a single modifier for the trait alias. Thus, we luckily don't need to handle the case where both final and the visibility can change.

[nielsdos]

Right, so now only this situation creates the warning (if it hadn't already warned earlier):

<?php

trait MyTrait {
    private function someMethod(): void {}
}

class Test {
    use MyTrait {
        someMethod as final anotherMethod;
    }
}

Note though that relaxing the warning might go against the copy+paste behaviour that traits try to mimick, as copy pasting with the editing visibility would generate a warning too. This was the point of introducing the warning. Anyway, I'm not really objecting.

[iluuu1994]

Note though that relaxing the warning might go against the copy+paste behaviour that traits try to mimick

That's a fair pair point. I think this is slightly different in that it the method isn't just copy&pasted, but also modified. Since we don't allow removing modifiers, it seems relaxing this warning would enable a reasonable use-case that worked previously, when you cannot remove final on the trait itself.

[nielsdos]

I guess it's a matter of perspective, I don't object.