src/ssd: allow invisible resize area across outputs

src/ssd: allow invisible resize area across outputs

This uses the new `view->outputs` bitset to calculate the intersection
with *all* outputs the view is currently visible on.

This ensures that the invisible resize handle works across outputs
while still making sure that it won't leak into neighboring ones just
because it is positioned closely to an output edge (either manually,
maximized or snapped via SnapToEdge or SnapToRegion).

Co-Authored-By: @johanmalm
Fixes: #1486
Reported-By: @lurch