Make seat_get_active_child ignore floating children

seat_get_active_child is used to get the active tiling child in a few
places, such as outputs getting their active workspace and
tabbed/stacked containers getting their visible child. When a workspace
uses a tabbed or stacked layout and contains a focused floating view,
calling seat_get_active_child on the workspace would incorrectly return
the floating view. This changes it so it will return the tiling child.

This fixes the following bug:

* Create layout T[view view] then float one of the views
* Attempt to click the tiling view to give it focus - it wouldn't work
because seat_get_active_child would return the floating view

sway/input/seat.c

@@ -888,10 +888,18 @@ struct sway_node *seat_get_active_child(struct sway_seat *seat,
 	struct sway_seat_node *current;
 	wl_list_for_each(current, &seat->focus_stack, link) {
 		struct sway_node *node = current->node;
-		if (node_get_parent(node) == parent) {
-			return node;
+		if (node_get_parent(node) != parent) {
+			continue;
+		}
+		if (parent->type == N_WORKSPACE) {
+			// Only consider tiling children
+			struct sway_workspace *ws = parent->sway_workspace;
+			if (list_find(ws->tiling, node->sway_container) == -1) {
+				continue;
 			}
 		}
+		return node;
+	}
 	return NULL;
 }