GH-15976: don't say "type alias" (#15996)

Follow-up to GH-15977

`zend_assert_valid_class_name()`: use double quotes around names (#15990)

GH-15976: clarify error messages for enum/trait/interface/alias names

Instead of always saying that a name is reserved or deprecated and
cannot/should not be used as a class name, take t

GH-15976: clarify error messages for enum/trait/interface/alias names

Instead of always saying that a name is reserved or deprecated and
cannot/should not be used as a class name, take the usage into account and say
the name cannot be used as an enum name, trait name, etc. In the process, for
class names add a missing "a".

show more ...

GH-15976: test current output

So that it is clearer what changes