Blender Git Loki

Nodes: separate node name and display name in bNodeTreePath

Previously, `node_name` was rarely actually a name of a node. It is set
correctly as node name in `ED_node_tree_push`. However, later on it
was overwritten by the name of an id data block in `node_draw_space`.

Now, the node_name stays the name of the "parent" node. Whereas
display_name is the name that will be displayed in the breadcrumbs.

With this change, the `node_name` can be used to reconstruct the
actual path from the root node tree to the currently visible tree.

Differential Revision: https://developer.blender.org/D10874