view: ensure that floating views don't overlap top panels

view: ensure that floating views don't overlap top panels

The top_left_edge_boundary_check() function in xwayland.c ensures that
views trying to position themselves at 0,0 don't end up with a titlebar
offscreen. However, it doesn't take into account the usable area and
thus these views can still end up overlapping a top panel.

Also, there is no good reason for top_left_edge_boundary_check() to be
xwayland-specific. This logic should really be part of
view_adjust_for_layout_change().

To fix all this, add a new view_adjust_floating_geometry() function,
which replaces the existing similar (and duplicated) logic in
view_apply_natural_geometry() and view_adjust_for_layout_change().

view_adjust_for_layout_change() is already being called from xwayland's
set_initial_position(), so top_left_edge_boundary_check() is now
redundant and can just be deleted.

Lightly tested with waybar and feh --geometry 640x480+0+0. The feh
window is now correctly positioned below waybar, even if started before
waybar (in that case, the feh window is moved when waybar starts).