Implement iterators per container type

This introduces the following `for_each` functions:

* root_for_each_workspace
* root_for_each_container
* output_for_each_workspace
* output_for_each_container
* workspace_for_each_container

And introduces the following `find` functions:

* root_find_output
* root_find_workspace
* root_find_container
* output_find_workspace
* output_find_container
* workspace_find_container
* container_find_child

And removes the following functions:

* container_descendants
* container_for_each_descendant
* container_find

This change is preparing the way for demoting sway_container. Eventually
these functions will accept and return sway_outputs, sway_workspaces and
sway_containers (meaning a C_CONTAINER or C_VIEW).

This change also makes it easy to handle abnormalities like the
workspace floating list, root's scratchpad list and (once implemented)
root's saved workspaces list for when there's no connected outputs.

include/sway/output.h

@@ -95,4 +95,16 @@ void output_drag_icons_for_each_surface(struct sway_output *output,
 	struct wl_list *drag_icons, sway_surface_iterator_func_t iterator,
 	void *user_data);
 
+void output_for_each_workspace(struct sway_container *output,
+		void (*f)(struct sway_container *con, void *data), void *data);
+
+void output_for_each_container(struct sway_container *output,
+		void (*f)(struct sway_container *con, void *data), void *data);
+
+struct sway_container *output_find_workspace(struct sway_container *output,
+		bool (*test)(struct sway_container *con, void *data), void *data);
+
+struct sway_container *output_find_container(struct sway_container *output,
+		bool (*test)(struct sway_container *con, void *data), void *data);
+
 #endif

include/sway/tree/container.h

@@ -214,15 +214,11 @@ struct sway_container *container_destroy(struct sway_container *container);
 
 struct sway_container *container_close(struct sway_container *container);
 
-void container_descendants(struct sway_container *root,
-		enum sway_container_type type,
-		void (*func)(struct sway_container *item, void *data), void *data);
-
 /**
  * Search a container's descendants a container based on test criteria. Returns
  * the first container that passes the test.
  */
-struct sway_container *container_find(struct sway_container *container,
+struct sway_container *container_find_child(struct sway_container *container,
 		bool (*test)(struct sway_container *view, void *data), void *data);
 
 /**
@@ -244,10 +240,7 @@ struct sway_container *tiling_container_at(
 		struct sway_container *con, double lx, double ly,
 		struct wlr_surface **surface, double *sx, double *sy);
 
-/**
- * Apply the function for each child of the container depth first.
- */
-void container_for_each_descendant(struct sway_container *container,
+void container_for_each_child(struct sway_container *container,
 		void (*f)(struct sway_container *container, void *data), void *data);
 
 /**

include/sway/tree/root.h

@@ -58,4 +58,19 @@ struct sway_container *root_workspace_for_pid(pid_t pid);
 
 void root_record_workspace_pid(pid_t pid);
 
+void root_for_each_workspace(void (*f)(struct sway_container *con, void *data),
+		void *data);
+
+void root_for_each_container(void (*f)(struct sway_container *con, void *data),
+		void *data);
+
+struct sway_container *root_find_output(
+		bool (*test)(struct sway_container *con, void *data), void *data);
+
+struct sway_container *root_find_workspace(
+		bool (*test)(struct sway_container *con, void *data), void *data);
+
+struct sway_container *root_find_container(
+		bool (*test)(struct sway_container *con, void *data), void *data);
+
 #endif

include/sway/tree/workspace.h

@@ -50,6 +50,12 @@ struct sway_container *workspace_output_get_highest_available(
 
 void workspace_detect_urgent(struct sway_container *workspace);
 
+void workspace_for_each_container(struct sway_container *ws,
+		void (*f)(struct sway_container *con, void *data), void *data);
+
+struct sway_container *workspace_find_container(struct sway_container *ws,
+		bool (*test)(struct sway_container *con, void *data), void *data);
+
 /**
  * Wrap the workspace's tiling children in a new container.
  * The new container will be the only direct tiling child of the workspace.