UI: Better support for linked data-blocks in search buttons

In RNA pointer search buttons (i.e. the ones with an eyedropper),
data-blocks were handled badly. It was not possible to select a linked
data-block that had the same name as a local one, which is especially
common with library overrides. Neither was there a hint to tell appart
linked data-blocks and which .blend file they come from.
These issues are addressed now, we show an "L" prefix and the .blend
file name in the search box (like in ID-templates).

Changes here are quite simple, since the heavy lifting was already done
through c20c203b82.

Addresses T73156.

source/blender/editors/interface/interface_utils.c

@@ -36,6 +36,7 @@
 
 #include "BLT_translation.h"
 
+#include "BKE_lib_id.h"
 #include "BKE_report.h"
 
 #include "MEM_guardedalloc.h"
@@ -395,11 +396,12 @@ void ui_rna_collection_search_cb(const struct bContext *C,
                                  uiSearchItems *items)
 {
   uiRNACollectionSearch *data = arg;
-  char *name;
   int i = 0, iconid = 0, flag = RNA_property_flag(data->target_prop);
   ListBase *items_list = MEM_callocN(sizeof(ListBase), "items_list");
   CollItemSearch *cis;
   const bool skip_filter = data->search_but && !data->search_but->changed;
+  char name_buf[UI_MAX_DRAW_STR];
+  char *name;
 
   /* build a temporary list of relevant items first */
   RNA_PROP_BEGIN (&data->search_ptr, itemptr, data->search_prop) {
@@ -417,24 +419,31 @@ void ui_rna_collection_search_cb(const struct bContext *C,
       }
     }
 
-    /* Could use the string length here. */
-    name = RNA_struct_name_get_alloc(&itemptr, NULL, 0, NULL);
-
     iconid = 0;
     if (itemptr.type && RNA_struct_is_ID(itemptr.type)) {
       iconid = ui_id_icon_get(C, itemptr.data, false);
+
+      BKE_id_full_name_ui_prefix_get(name_buf, itemptr.data);
+      BLI_STATIC_ASSERT(sizeof(name_buf) >= MAX_ID_FULL_NAME_UI,
+                        "Name string buffer should be big enough to hold full UI ID name");
+      name = name_buf;
+    }
+    else {
+      name = RNA_struct_name_get_alloc(&itemptr, name_buf, sizeof(name_buf), NULL);
     }
 
     if (name) {
       if (skip_filter || BLI_strcasestr(name, str)) {
         cis = MEM_callocN(sizeof(CollItemSearch), "CollectionItemSearch");
         cis->data = itemptr.data;
-        cis->name = MEM_dupallocN(name);
+        cis->name = BLI_strdup(name);
         cis->index = i;
         cis->iconid = iconid;
         BLI_addtail(items_list, cis);
       }
-      MEM_freeN(name);
+      if (name != name_buf) {
+        MEM_freeN(name);
+      }
     }
 
     i++;