This patch adds an integer identifier to nodes that doesn't change when
the node name changes. This identifier can be used by different systems
to reference a node. This may be important to store caches and simulation
states per node, because otherwise those would always be invalidated
when a node name changes.
Additionally, this kind of identifier could make some things more efficient,
because with it an integer is enough to identify a node and one does not
have to store the node name.
I observed a 10% improvement in evaluation time in a file with an extreme
number of simple math nodes, due to reduced logging overhead-- from
0.226s to 0.205s.
Differential Revision: https://developer.blender.org/D15775
90ea1b7643