Improve final/abstract methods in interfaces error messages

[iluuu1994]

Closes #81683

[iluuu1994]

Not sure if this should fixed in master, PHP-8.0 or PHP-8.1.

[nikic]

PHP-8.1 sounds right.

[TysonAndre]

========DIFF========
001+ Fatal error: Interface method test::test() must not be final in C:\projects\php-src\Zend\tests\bug71871.php on line 4
001- Fatal error: Access type for interface method test::test() must be public in %s on line %d
========DONE========
FAIL Bug #71871: Interfaces allow final and abstract functions [C:\projects\php-src\Zend\tests\bug71871.phpt] 
PASS bug #71428.1: inheritance with null default values [C:\projects\php-src\Zend\tests\bug71428.1.phpt] 
                                                     
========DIFF========
001+ Fatal error: Interface method test::test() must not be abstract in C:\projects\php-src\Zend\tests\bug71871_2.php on line 4
001- Fatal error: Access type for interface method test::test() must be public in %s on line %d
========DONE========
FAIL Bug #71871: Interfaces allow final and abstract functions [C:\projects\php-src\Zend\tests\bug71871_2.phpt]

We already have some tests that (1) need to be updated and (2) may make new tests redundant. lgtm otherwise