Redraw only the spinner when nothing else has changed (#5571)

### PR Description
This fixes #4734, where lazygit would use a lot of CPU when the spinner
was shown due to redrawing the entire screen every time the spinner
needed a redraw.
The change adds the ability to request a UI redraw without invalidating
the full UI, thus only redrawing the spinner, re-routing the spinner to
this new flow.
CPU usage on a chromebook went from 60% to 5% when the spinner is shown.

Changing the refresh rate of the spinner from 50ms to 200ms brings it
down from 5% to 1% if ever we would like to change the default,
personally I prefer the slower moving spinner, but that's subjective.