Blender Git Loki

UI: Support right aligned non-shortcut hints in widgets

Widget drawing code already supported drawing right-aligned, grayed out
shortcut strings. This patch generalizes things a bit so this can also
be used to draw other hints in the same way. There have been a few
instances in the past where this would've been useful, D11046 being the
latest one.

Note that besides some manual regression testing, I didn't check if this
works yet, as there is no code actually using it (other than the
shortcuts). Can be checked as part of further development for D11046.

A possible further improvement would be providing a way to define how
clipping should be done. E.g. sometimes the right-aligned text should be
clipped first (because it's just a hint), in other cases it should be
left untouched (like current code explicitly does it for shortcuts).

Removes the `UI_BUT_HAS_SHORTCUT` flag, which isn't needed anymore.