Cleanup: Put Outliner C++ namespace into `blender::ed` namespace, add comments

See https://developer.blender.org/D9499.

Also remove unnecessary forward declaration.

source/blender/editors/space_outliner/outliner_intern.h

@@ -47,6 +47,9 @@ struct wmKeyConfig;
 struct wmOperatorType;
 
 typedef struct SpaceOutliner_Runtime {
+  /**
+   * Internal C++ object to create and manage the tree for a specific display type (View Layers,
+   * Scenes, Blender File, etc.). */
   struct TreeView *tree_view;
 } SpaceOutliner_Runtime;
 

source/blender/editors/space_outliner/tree/tree_view.cc

@@ -24,9 +24,9 @@
 
 #include "tree_view.hh"
 
-namespace outliner = blender::outliner;
+namespace outliner = blender::ed::outliner;
 /* Convenience. */
-using blender::outliner::AbstractTreeView;
+using outliner::AbstractTreeView;
 
 TreeView *outliner_tree_view_create(eSpaceOutliner_Mode mode, SpaceOutliner *space_outliner)
 {

source/blender/editors/space_outliner/tree/tree_view.hh

@@ -25,7 +25,6 @@
 
 #include "DNA_space_types.h"
 
-struct bContext;
 struct ListBase;
 struct SpaceOutliner;
 struct TreeElement;
@@ -34,6 +33,7 @@ struct TreeSourceData;
 #ifdef __cplusplus
 
 namespace blender {
+namespace ed {
 namespace outliner {
 
 using Tree = ListBase;
@@ -42,6 +42,8 @@ using Tree = ListBase;
 /* Tree-View Interface */
 
 /**
+ * \brief Base Class For Tree-Views
+ *
  * Abstract base class defining the interface for tree-view variants. For each Outliner display
  * type (e.g View Layer, Scenes, Blender File), a derived class implements a #buildTree() function,
  * that based on Blender data (#TreeSourceData), builds a custom tree of whatever data it wants to
@@ -68,6 +70,9 @@ class AbstractTreeView {
 /* -------------------------------------------------------------------- */
 /* View Layer Tree-View */
 
+/**
+ * \brief Tree-View for the View Layer display mode.
+ */
 class TreeViewViewLayer final : public AbstractTreeView {
   ViewLayer *_view_layer = nullptr;
   bool _show_objects = true;
@@ -85,6 +90,7 @@ class TreeViewViewLayer final : public AbstractTreeView {
 };
 
 }  // namespace outliner
+}  // namespace ed
 }  // namespace blender
 
 extern "C" {

source/blender/editors/space_outliner/tree/tree_view_view_layer.cc

@@ -35,6 +35,7 @@
 #include "tree_view.hh"
 
 namespace blender {
+namespace ed {
 namespace outliner {
 
 /* Convenience/readability. */
@@ -283,4 +284,5 @@ void ObjectsChildrenBuilder::make_object_parent_hierarchy_collections()
 /** \} */
 
 }  // namespace outliner
+}  // namespace ed
 }  // namespace blender