wayland: optionally disable pointer input on subsurfaces

We have a number of sub-surfaces for which we are *not* interrested in
pointer (or touch) input.

Up until now, we’ve manually dealt with these, by recognizing these
surfaces in all pointer events, and ignoring them.

But, lo and behold, there are better ways of doing this. By clearing
the subsurface’s input region, the compositor will do this for us -
when a pointer is outside a surface’s input region, the event is
passed to the next surface underneath it.

This is exactly what we want! Do this for all subsurfaces, *except*
the CSDs.

terminal.h

@@ -272,10 +272,6 @@ struct ptmx_buffer {
 enum term_surface {
     TERM_SURF_NONE,
     TERM_SURF_GRID,
-    TERM_SURF_SEARCH,
-    TERM_SURF_SCROLLBACK_INDICATOR,
-    TERM_SURF_RENDER_TIMER,
-    TERM_SURF_JUMP_LABEL,
     TERM_SURF_TITLE,
     TERM_SURF_BORDER_LEFT,
     TERM_SURF_BORDER_RIGHT,