[php2cpg] Resolve static method call name when called by self

[wunused]

When a static method call is made by referring to self, the AST node created for it failed to resolve the proper method full name.

For example:

<?php
class Foo {
    static function bar($x) {
        return 0;
    }
    function baz($x) {
        self::bar($x);
    }
}

The method full name of the call node for self::bar($x) is self::bar, but it should be Foo::bar.

This PR resolves the method full name of functions called by self.

[DavidBakerEffendi]

If you want to leave in commented-out code, then please supply a note

[wunused]

Sorry, and thanks for the catch - this comment has been removed.

[DavidBakerEffendi]

Will approve once commented-out code is addressed

[DavidBakerEffendi]

Approving since this seems sound to me