UI: Allow view items to not be activatable

No user visible changes expected.

In some cases you'd want a view in which no, or not all items can be
activated. Needed for #104831, but makes sense as a general feature for
UI view items.

source/blender/editors/include/UI_abstract_view.hh

@@ -139,6 +139,7 @@ class AbstractViewItem {
    * If this wasn't done, the behavior of items is undefined.
    */
   AbstractView *view_ = nullptr;
+  bool is_activatable_ = true;
   bool is_interactive_ = true;
   bool is_active_ = false;
   bool is_renaming_ = false;
@@ -196,6 +197,8 @@ class AbstractViewItem {
   void disable_interaction();
   bool is_interactive() const;
 
+  void disable_activatable();
+
   /**
    * Requires the view to have completed reconstruction, see #is_reconstructed(). Otherwise we
    * can't be sure about the item state.

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

@@ -227,6 +227,11 @@ AbstractView &AbstractViewItem::get_view() const
   return *view_;
 }
 
+void AbstractViewItem::disable_activatable()
+{
+  is_activatable_ = false;
+}
+
 void AbstractViewItem::disable_interaction()
 {
   is_interactive_ = false;

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

@@ -175,6 +175,9 @@ void AbstractGridViewItem::activate()
   BLI_assert_msg(get_view().is_reconstructed(),
                  "Item activation can't be done until reconstruction is completed");
 
+  if (!is_activatable_) {
+    return;
+  }
   if (is_active()) {
     return;
   }

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

@@ -301,6 +301,9 @@ void AbstractTreeViewItem::activate()
   BLI_assert_msg(get_tree_view().is_reconstructed(),
                  "Item activation can't be done until reconstruction is completed");
 
+  if (!is_activatable_) {
+    return;
+  }
   if (is_active()) {
     return;
   }