Previously, the owner-id on localized node trees, like the one created in
`GPU_material_from_nodetree` would have `bNodeTree::owner_id` set, even though
they were independent. The leads to asserts when using `BKE_id_owner_get` on the
localized node tree.
The `node_tree_localize` already took a `ID *new_owner_id` parameter. However,
if it was `nullptr` it was ignored instead actually clearing the `owner_id`.
This patch changes the parameter to `std::optional<ID *> new_owner_id`. Now,
`std::nullopt` means that the value is ignored and when `nullptr` is passed in,
the `owner_id` will be cleared on the localized tree.
Since `node_tree_localize` indirectly uses other functions, the same function
signature change is done in `BKE_libblock_copy_in_lib` and `BKE_id_copy_in_lib`.
The callers have been updated to pass in `nullopt` instead of `nullptr`.
Pull Request: https://projects.blender.org/blender/blender/pulls/133002
11f20683f9