UI: Add function to query debug name of view items

No user visible change expected.

There's no good way to identify items from their base class which is
annoying for development/debugging. I ended up adding a helper like this
a few times, so makes sense to just add this to the API.

source/blender/editors/include/UI_abstract_view.hh

@@ -212,6 +212,13 @@ class AbstractViewItem {
    */
   virtual std::unique_ptr<DropTargetInterface> create_item_drop_target();
 
+  /**
+   * View types should implement this to return some name or identifier of the item, which is
+   * helpful for debugging (there's nothing to identify the item just from the #AbstractViewItem
+   * otherwise).
+   */
+  virtual std::optional<std::string> debug_name() const;
+
   /** Return the result of #is_filtered_visible(), but ensure the result is cached so it's only
    * queried once per redraw. */
   bool is_filtered_visible_cached() const;

source/blender/editors/include/UI_grid_view.hh

@@ -47,6 +47,8 @@ class AbstractGridViewItem : public AbstractViewItem {
 
   virtual void build_grid_tile(uiLayout &layout) const = 0;
 
+  /* virtual */ std::optional<std::string> debug_name() const override;
+
   AbstractGridView &get_view() const;
 
  protected:

source/blender/editors/include/UI_tree_view.hh

@@ -187,6 +187,8 @@ class AbstractTreeViewItem : public AbstractViewItem, public TreeViewItemContain
 
   virtual void build_row(uiLayout &row) = 0;
 
+  /* virtual */ std::optional<std::string> debug_name() const override;
+
   std::unique_ptr<DropTargetInterface> create_item_drop_target() final;
   virtual std::unique_ptr<TreeViewItemDropTarget> create_drop_target();
 

source/blender/editors/interface/views/abstract_view_item.cc

@@ -269,6 +269,11 @@ std::unique_ptr<DropTargetInterface> AbstractViewItem::create_item_drop_target()
   return nullptr;
 }
 
+std::optional<std::string> AbstractViewItem::debug_name() const
+{
+  return {};
+}
+
 AbstractViewItemDragController::AbstractViewItemDragController(AbstractView &view) : view_(view) {}
 
 void AbstractViewItemDragController::on_drag_start()

source/blender/editors/interface/views/grid_view.cc

@@ -163,6 +163,11 @@ void AbstractGridViewItem::add_grid_tile_button(uiBlock &block)
   UI_but_func_set(view_item_but_, grid_tile_click_fn, view_item_but_, nullptr);
 }
 
+std::optional<std::string> AbstractGridViewItem::debug_name() const
+{
+  return identifier_;
+}
+
 AbstractGridView &AbstractGridViewItem::get_view() const
 {
   if (UNLIKELY(!view_)) {

source/blender/editors/interface/views/tree_view.cc

@@ -456,6 +456,11 @@ std::unique_ptr<TreeViewItemDropTarget> AbstractTreeViewItem::create_drop_target
   return nullptr;
 }
 
+std::optional<std::string> AbstractTreeViewItem::debug_name() const
+{
+  return label_;
+}
+
 AbstractTreeView &AbstractTreeViewItem::get_tree_view() const
 {
   return dynamic_cast<AbstractTreeView &>(get_view());