Code is simpler when the uiBlocks used during drawing are simply
stored in an array. Additionally, looping can be simpler when we use
an vector to hold a temporary copy of the tree's linked list of nodes.
This patch also slightly changes how uiBlocks are "named" in
`node_uiblocks_init`. Now it uses the node name instead of the
pointer, which is helpful so we rely less on the node's address.
Differential Revision: https://developer.blender.org/D13540
d56bbfea7b