Rename a few functions to more accurately express their intent:
- `sequence_handle_size_get_clamped()` ->`strip_handle_draw_size_get()`
- `clickable_handle_size_get()` -> `inner_clickable_handle_size_get()`
Additionally:
- Move check for making strips unclickable when they are short enough in
the vertical direction from `sequencer_main_cursor()` to
`ED_sequencer_get_handle()`.
- Use `inner_clickable_handle_size_get()` in box select with handles.
- Add clarifying comments that calculate exact handle sizes.
There should be no functional changes (barring a tiny change in box
select with handle calculation).
0141bbb71c