Generally, node names are expected to be unique within a node tree. However,
`ntree_shader_copy_branch` currently does not enforce this for performance
reasons. This was broken by recent changes in 5b73f798d0 and 9fd877e174 which
allows for passing already unique names and identifiers to the node copy
function.
The main problem here was that the `use_unique` parameter of the `node_copy`
function was not well defined. Now, this function is completely removed in favor
of using `node_copy_with_mapping` directly. This also has a new
`allow_duplicate_names` parameter now which makes the expected behavior more
explicit.
Pull Request: https://projects.blender.org/blender/blender/pulls/143951
8133f7aa13