WIP: BKE_lib_query: Add a partial ID usage iterator system.

The idea is to allow iterating over e.g. all ID usages of a node from a
whole nodetree, using the same generic handling as existing 'whole ID'
`foreach_id` code.

This is necessary in some cases wher a sub-data needs to processed
independently from any 'owner ID', e.g. in some copy/paste handling.

This is a pre-requirement for proper fix of nodes copy/paste (see
e.g. #120103).

@@ -26,2 +28,4 @@
 namespace blender::ed::space_node {
 
+struct NodeClipboardItemIDInfo {
+  /* Name and library filepath form a unique identifer for a given ID. */

@@ -27,1 +29,4 @@
 
+struct NodeClipboardItemIDInfo {
+  /* Name and library filepath form a unique identifer for a given ID. */
+  std::string id_name = "";

@@ -28,0 +30,4 @@
+struct NodeClipboardItemIDInfo {
+  /* Name and library filepath form a unique identifer for a given ID. */
+  std::string id_name = "";
+  /* Note: Library reference is stored as an absolute path. Since the Node clippboard is runtime

@@ -58,0 +81,4 @@
+   *
+   * DO NOT update the nodes' pointers here though, as this would affect the clipboard content,
+   * which is no desired here. It should remain as in original state, such that e.g. one can copy
+   * nodes in file `A.blend`, open file `B.blend`, paste nodes (and lose some of the invlaid ID

@@ -83,0 +111,4 @@
+     * and libpath pairs can be used here.
+     *   - UID cannot be trusted accross file load.
+     *   - ID pointer itself cannot be trusted accross undo/redo and fileload. */
+    auto validate_id_fn = [this, &is_valid, &bmain, &bmain_id_map, &libraries_path_to_id](