Currently Annotation.draw goes through _check_xy to check whether the
annotation should be drawn at all, and then through
_update_position_xytext to position itself. In order to save a single
call to _get_position_xy, it first calls _get_position_xy itself and
then passes it down to the helper functions, making them harder to
follow. Instead, just let _check_xy call _get_position_xy itself (and
even then, this is only needed for some values of annotation_clip), and
likewise for _update_position_xytext (which just becomes a call to
update_positions).

Also a small shortening of Text.update_bbox_position_size.

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way