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.

source/blender/editors/include/UI_interface.h

@@ -290,18 +290,14 @@ enum {
   /** Active right part of number button */
   UI_BUT_ACTIVE_RIGHT = 1 << 22,
 
-  /* (also used by search buttons to enforce shortcut display for their items). */
-  /** Button has shortcut text. */
-  UI_BUT_HAS_SHORTCUT = 1 << 23,
-
   /** Reverse order of consecutive off/on icons */
-  UI_BUT_ICON_REVERSE = 1 << 24,
+  UI_BUT_ICON_REVERSE = 1 << 23,
 
   /** Value is animated, but the current value differs from the animated one. */
-  UI_BUT_ANIMATED_CHANGED = 1 << 25,
+  UI_BUT_ANIMATED_CHANGED = 1 << 24,
 
   /* Draw the checkbox buttons inverted. */
-  UI_BUT_CHECKBOX_INVERT = 1 << 26,
+  UI_BUT_CHECKBOX_INVERT = 1 << 25,
 };
 
 /* scale fixed button widths by this to account for DPI */