UI: Display ID counts when dragging multiple objects

When multiple selected object/collections are dragged from outliner,
their tooltip shows "objects/collections" as plural. As proposed by Harley,
display selected id counts in tooltip ("3 objects" for example).
Changed return type to string for `WM_drag_get_item_name`. That way,
we don't have to worry about freeing char pointer memory manually.

Resolves #139737

See PR description for images

Pull Request: https://projects.blender.org/blender/blender/pulls/139770

source/blender/editors/interface/interface_dropboxes.cc

@@ -132,7 +132,7 @@ static std::string ui_drop_material_tooltip(bContext *C,
 
   PointerRNA rna_prev_material = RNA_pointer_get(&mat_slot, "material");
   Material *prev_mat_in_slot = static_cast<Material *>(rna_prev_material.data);
-  const char *dragged_material_name = WM_drag_get_item_name(drag);
+  const std::string dragged_material_name = WM_drag_get_item_name(drag);
 
   if (prev_mat_in_slot) {
     return fmt::format(fmt::runtime(TIP_("Drop {} on slot {} (replacing {}) of {}")),

source/blender/editors/screen/screen_ops.cc

@@ -7372,7 +7372,7 @@ static std::string screen_drop_scene_tooltip(bContext * /*C*/,
                                                  [2],
                                              wmDropBox * /*drop*/)
 {
-  const char *dragged_scene_name = WM_drag_get_item_name(drag);
+  const std::string dragged_scene_name = WM_drag_get_item_name(drag);
   wmDragAsset *asset_drag = WM_drag_get_asset_data(drag, ID_SCE);
   if (asset_drag) {
     switch (asset_drag->import_settings.method) {

source/blender/editors/space_view3d/view3d_dropboxes.cc

@@ -207,13 +207,13 @@ static std::string view3d_mat_drop_tooltip(bContext *C,
                                            const int xy[2],
                                            wmDropBox * /*drop*/)
 {
-  const char *name = WM_drag_get_item_name(drag);
+  const std::string name = WM_drag_get_item_name(drag);
   ARegion *region = CTX_wm_region(C);
   const int mval[2] = {
       xy[0] - region->winrct.xmin,
       xy[1] - region->winrct.ymin,
   };
-  return ed::object::drop_named_material_tooltip(C, name, mval);
+  return ed::object::drop_named_material_tooltip(C, name.c_str(), mval);
 }
 
 static bool view3d_world_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)

source/blender/windowmanager/WM_api.hh

@@ -1749,7 +1749,7 @@ void WM_drag_add_asset_list_item(wmDrag *drag, const asset_system::AssetRepresen
 
 const ListBaseT<wmDragAssetListItem> *WM_drag_asset_list_get(const wmDrag *drag);
 
-const char *WM_drag_get_item_name(wmDrag *drag);
+const std::string WM_drag_get_item_name(wmDrag *drag);
 
 /* Paths drag and drop. */
 /**

source/blender/windowmanager/intern/wm_dragdrop.cc

@@ -1027,31 +1027,31 @@ static void wm_drop_redalert_draw(const StringRef redalert_str, int x, int y)
   ui::fontstyle_draw_simple_backdrop(fstyle, x, y, redalert_str, col_fg, col_bg);
 }
 
-const char *WM_drag_get_item_name(wmDrag *drag)
+const std::string WM_drag_get_item_name(wmDrag *drag)
 {
   switch (drag->type) {
     case WM_DRAG_ID: {
       ID *id = WM_drag_get_local_ID(drag, 0);
-      bool single = BLI_listbase_is_single(&drag->ids);
+      const int dragged_ids = BLI_listbase_count(&drag->ids);
 
-      if (single) {
+      if (dragged_ids == 1) {
         return id->name + 2;
       }
       if (id) {
-        return BKE_idtype_idcode_to_name_plural(GS(id->name));
+        return std::to_string(dragged_ids) + " " + BKE_idtype_idcode_to_name_plural(GS(id->name));
       }
       break;
     }
     case WM_DRAG_ASSET: {
       const wmDragAsset *asset_drag = WM_drag_get_asset_data(drag, 0);
-      return asset_drag->asset->get_name().c_str();
+      return asset_drag->asset->get_name();
     }
     case WM_DRAG_PATH: {
       const wmDragPath *path_drag_data = static_cast<const wmDragPath *>(drag->poin);
-      return path_drag_data->tooltip.c_str();
+      return path_drag_data->tooltip;
     }
     case WM_DRAG_NAME:
-      return static_cast<const char *>(drag->poin);
+      return *static_cast<const std::string *>(drag->poin);
     default:
       break;
   }
@@ -1134,7 +1134,7 @@ static void wm_drag_draw_item_name(wmDrag *drag, const int x, const int y)
 {
   const uiFontStyle *fstyle = UI_FSTYLE_WIDGET;
   const uchar text_col[] = {255, 255, 255, 255};
-  ui::fontstyle_draw_simple(fstyle, x, y, WM_drag_get_item_name(drag), text_col);
+  ui::fontstyle_draw_simple(fstyle, x, y, WM_drag_get_item_name(drag).c_str(), text_col);
 }
 
 void WM_drag_draw_item_name_fn(bContext * /*C*/, wmWindow *win, wmDrag *drag, const int xy[2])