Move view {x,y,width,height} into container struct

This renames/moves the following properties:

* sway_view.{x,y,width,height} ->
sway_container.content_{x,y,width,height}
    * This is required to support placeholder containers as they don't
    have a view.
* sway_container_state.view_{x,y,width,height} ->
sway_container_state.content_{x,y,width,height}
    * To remain consistent with the above.
* sway_container_state.con_{x,y,width,height} ->
sway_container_state.{x,y,width,height}
    * The con prefix was there to give it contrast from the view
    properties, and is no longer useful.

The function container_set_geometry_from_floating_view has also been
renamed to container_set_geometry_from_content.

include/sway/tree/view.h

@@ -67,10 +67,6 @@ struct sway_view {
 
 	pid_t pid;
 
-	// Geometry of the view itself (excludes borders) in layout coordinates
-	double x, y;
-	int width, height;
-
 	double saved_x, saved_y;
 	int saved_width, saved_height;