desktop-shell: Port to libweston-desktop

All the shell protocol details, Xwayland glue and popups (and their
grab) are now handled in libweston-desktop.
Fullscreen methods (for wl_shell) are removed for now.

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>
Acked-by: Giulio Camuffo <giulio.camuffo@kdab.com>

Differential Revision: https://phabricator.freedesktop.org/D1209

shared/helpers.h

@@ -52,6 +52,17 @@ extern "C" {
 #define MIN(x,y) (((x) < (y)) ? (x) : (y))
 #endif
 
+/**
+ * Returns the bigger of two values.
+ *
+ * @param x the first item to compare.
+ * @param y the second item to compare.
+ * @return the value that evaluates to more than the other.
+ */
+#ifndef MAX
+#define MAX(x,y) (((x) > (y)) ? (x) : (y))
+#endif
+
 /**
  * Returns a pointer the the containing struct of a given member item.
  *