LibQuery: Add option to NOT process embedded IDs.

Request from depsgraph department, which does basically consider those
embedded IDs as any other data-block (unlike any BKE ID management code).

source/blender/blenkernel/BKE_lib_query.h

@@ -116,6 +116,8 @@ enum {
   IDWALK_READONLY = (1 << 0),
   IDWALK_RECURSE = (1 << 1),    /* Also implies IDWALK_READONLY. */
   IDWALK_INCLUDE_UI = (1 << 2), /* Include UI pointers (from WM and screens editors). */
+  /** Do not process ID pointers inside embedded IDs. Needed by depsgraph processing e.g. */
+  IDWALK_IGNORE_EMBEDDED_ID = (1 << 3),
 
   IDWALK_NO_INDIRECT_PROXY_DATA_USAGE = (1 << 8), /* Ugly special case :(((( */
 };

source/blender/blenkernel/intern/lib_query.c

@@ -534,7 +534,10 @@ static void library_foreach_ID_as_subdata_link(ID **id_pp,
   FOREACH_CALLBACK_INVOKE_ID_PP(data, id_pp, IDWALK_CB_EMBEDDED);
   BLI_assert(id == *id_pp);
 
-  if (flag & IDWALK_RECURSE) {
+  if (flag & IDWALK_IGNORE_EMBEDDED_ID) {
+    /* Do Nothing. */
+  }
+  else if (flag & IDWALK_RECURSE) {
     /* Defer handling into main loop, recursively calling BKE_library_foreach_ID_link in
      * IDWALK_RECURSE case is troublesome, see T49553. */
     /* XXX note that this breaks the 'owner id' thing now, we likely want to handle that