Blender Git Loki

ID Creation: generate `session_uuid` in more cases.

Previous code would not generate a session uuid for embedded IDs (like
root node trees or master collections). While this is not a problem
currently since those are not directly stored in Main data-base, this is
conceptually wrong, since those IDs still pertain the Main data.

Further more, this is blocking using `session_uuid` more in depsgraph in
place from ID pointer itself, as identifier (related to T84397).