Fix #141882: Undo with local asset in asset shelf crashes Blender (ASAN)

Replace a `StringRef` with `std::string`, so that a copy is made of the
grid item identifier.

This identifier is used on redraw, to correlate the newly-drawn items
with items from the previous redraw. Using a `StringRef` here was
problematic when there's local assets, as those can be freed & re-built
(which in the case of the report happens on save/undo). Because of this,
the reference got corrupted, and the map lookup would fail. The "old
items" map now has a copy of the identifier, ensuring it is independent
of the data it represents.

Co-authored by Julian Eisel.

Pull Request: https://projects.blender.org/blender/blender/pulls/141888

source/blender/editors/include/UI_grid_view.hh

@@ -39,8 +39,12 @@ class AbstractGridViewItem : public AbstractViewItem {
   friend class GridViewLayoutBuilder;
 
  protected:
-  /** Reference to a string that uniquely identifies this item in the view. */
-  StringRef identifier_{};
+  /**
+   * A string that uniquely identifies this item in the view.
+   *
+   * Ideally this would just be a StringRef to save memory. This was made a
+   * std::string to fix #141882 in a relatively safe way. */
+  std::string identifier_{};
 
  public:
   /* virtual */ ~AbstractGridViewItem() override = default;