view: Add view_reload_ssd()

Gather related logic from `reload_config_and_theme()` in `server.c` and
`ssd_reload()` in `ssd.c` into a new function, `view_reload_ssd()`.

Also drop the `view->mapped` check since we want to update any view that
has SSD nodes created, mapped or not.

src/view.c

@@ -871,6 +871,16 @@ view_update_app_id(struct view *view)
 		view->toplevel_handle, app_id);
 }
 
+void
+view_reload_ssd(struct view *view)
+{
+	assert(view);
+	if (view->ssd_enabled) {
+		ssd_destroy(view);
+		ssd_create(view);
+	}
+}
+
 void
 view_destroy(struct view *view)
 {