cursor: add cursor_update_focus()

...and call it from desktop_move_to_front() in order force an enter event
on the surface below the cursor when cycling views.

Inspired by PR #164 - just restructured it a bit.

Suggested-by: @bi4k8

include/labwc.h

@@ -441,6 +441,15 @@ void cursor_rebase(struct seat *seat, uint32_t time_msec);
  * @cursor_name - name of cursor, for example "left_ptr" or "grab"
  */
 void cursor_set(struct seat *seat, const char *cursor_name);
+
+/**
+ * cursor_update_focus - update cursor focus
+ * @server - server
+ * Use it to force an update of the cursor icon and to send an enter event
+ * to the surface below the cursor.
+ */
+void cursor_update_focus(struct server *server);
+
 void cursor_init(struct seat *seat);
 
 void keyboard_init(struct seat *seat);

src/cursor.c

@@ -256,6 +256,20 @@ process_cursor_motion(struct server *server, uint32_t time)
 	}
 }
 
+static uint32_t
+msec(const struct timespec *t)
+{
+	return t->tv_sec * 1000 + t->tv_nsec / 1000000;
+}
+
+void
+cursor_update_focus(struct server *server)
+{
+	struct timespec now;
+	clock_gettime(CLOCK_MONOTONIC, &now);
+	process_cursor_motion(server, msec(&now));
+}
+
 void
 start_drag(struct wl_listener *listener, void *data)
 {

src/desktop.c

@@ -61,6 +61,7 @@ desktop_move_to_front(struct view *view)
 #if HAVE_XWAYLAND
 	move_xwayland_sub_views_to_front(view);
 #endif
+	cursor_update_focus(view->server);
 }
 
 static void