Teach `glib-mkenums` how to parse and ignore:
- `GLIB_AVAILABLE_ENUMERATOR_IN_x_xx`
- `GLIB_DEPRECATED_ENUMERATOR_IN_x_xx`
- `GLIB_DEPRECATED_ENUMERATOR_IN_x_xx_FOR(x)`
Future work could expose the deprecation/availability information as
substitutions in the template file, but this commit does not do that.
It does, however, add some unit tests for the annotations.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Fixes: #2327