Support for final constants

[weirdan]

https://psalm.dev/r/867638ab8b?php=8.1

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/867638ab8b

<?php

class A
{
    final const BAR = 'BAZ';
}

class B extends A {
    const BAR = 'BUZZ';
}

Psalm output (using commit 5aa06ae):

INFO: LessSpecificClassConstantType - 9:11 - The type ''BUZZ'' for B::BAR is more general than the type ''BAZ'' inherited from A::BAR

INFO: UnusedClass - 8:7 - Class B is never used

[weirdan]

Fixed by #7666