compositor: fix comments about weston_compositor::surface_list

a7af70436b converted the surface list into
a view list. There is no weston_compositor::surface_list anymore.

It looks like weston_surface::output's comment about surface list does
not apply to view list. Still, many places assume weston_surface::output
is not NULL when processing "visible" surfaces, e.g. those reachable via
the view list.

The comment on weston_view::output is updated. It seems there is no
longer any requirement for it to be NULL if the view is not in
view_list.

weston_view::link is documented to be in weston_compositor::view_list,
and weston_compositor::view_list is documented to contain weston_views.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Armin Krezović <krezovic.armin@gmail.com>
[Pekka: removed also the other "Must be NULL" comment.]

src/compositor.h

@@ -754,7 +754,7 @@ struct weston_compositor {
 	struct wl_list output_list;
 	struct wl_list seat_list;
 	struct wl_list layer_list;
-	struct wl_list view_list;
+	struct wl_list view_list;	/* struct weston_view::link */
 	struct wl_list plane_list;
 	struct wl_list key_binding_list;
 	struct wl_list modifier_binding_list;
@@ -890,7 +890,7 @@ struct weston_view {
 	struct wl_list surface_link;
 	struct wl_signal destroy_signal;
 
-	struct wl_list link;
+	struct wl_list link;             /* weston_compositor::view_list */
 	struct weston_layer_entry layer_link; /* part of geometry */
 	struct weston_plane *plane;
 
@@ -951,7 +951,6 @@ struct weston_view {
 	/*
 	 * Which output to vsync this surface to.
 	 * Used to determine, whether to send or queue frame events.
-	 * Must be NULL, if 'link' is not in weston_compositor::surface_list.
 	 */
 	struct weston_output *output;
 
@@ -1021,7 +1020,6 @@ struct weston_surface {
 	/*
 	 * Which output to vsync this surface to.
 	 * Used to determine, whether to send or queue frame events.
-	 * Must be NULL, if 'link' is not in weston_compositor::surface_list.
 	 */
 	struct weston_output *output;