view: try to honor original geometry with layout changes

view: try to honor original geometry with layout changes

Whenever the output layout changes, each view's original geometry will
be captured as last_layout_geometry (if it has not already been captured
by a previous layout change), which will remain valid unless the user
modifies the view's geometry (i.e., by tiling, maximizing, moving,
resizing or full-screening). On subsequent output layout changes, views
with valid last_layout_geometry will be back to their original position
if possible, or else to the closest possible output.