Implement <resize><drawContents>

<resize><drawContents>[yes|no] configures whether to let the clients
redraw its window content content while resizing.

When <resize><drawContents> is set to no, a multi-rect is shown to
indicate the geometry of the resized window.

src/meson.build

@@ -20,6 +20,7 @@ labwc_sources = files(
   'placement.c',
   'regions.c',
   'resistance.c',
+  'resize-outlines.c',
   'seat.c',
   'server.c',
   'session-lock.c',