Add input and bounding shapes support (#2742)

Basic idea: if the window has a shape, set the parent container shape as
the union of the window shape and the shape of the frame borders.

Co-authored-by: Uli Schlachter <psychon@znc.in>

include/data.h

@@ -484,6 +484,11 @@ struct Window {
     /* aspect ratio from WM_NORMAL_HINTS (MPlayer uses this for example) */
     double min_aspect_ratio;
     double max_aspect_ratio;
+
+    /** The window has a nonrectangular shape. */
+    bool shaped;
+    /** The window has a nonrectangular input shape. */
+    bool input_shaped;
 };
 
 /**