vsync: choose vsync method automatically

Choose the best vsync method for the user, instead of asking them to
frustratingly try every one of the options to see what works.

With this commit, the `vsync` option will take only a boolean value.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/common.h

@@ -526,6 +526,8 @@ typedef struct session {
 	// === DBus related ===
 	void *dbus_data;
 #endif
+
+	int (*vsync_wait)(session_t *);
 } session_t;
 
 /// Temporary structure used for communication between