Prevent classes and methods from declared both final and abstract

[pierredup]

• bug fix? Yes
• BC break? yes
• doc PR: N/A

Classes and methods cannot be declared final and abstract. This will now throw an exception if you try to generate a final abstract class or method. It's a BC break because of the new exception, but the generated code would never have been valid, so I doubt there is any use that will break

[dg]

It's probably better to check it when the code is generated, to allow this anytime:

$class->setAbstract(true)->setFinal(false);

ie. in cases when $class is already marked as final