Blender Git Loki

Geometry Nodes: Refactor / fix point separate node

The point separate node was failing in situations where one of the
outputs was empty. In addition, the code was not structured very well.
This new implementation stores less temporary information, is more
geometry component type agnostic, and is more self-descriptive.
It also solves the problems mentioned above.

Fixes T86573

Differential Revision: https://developer.blender.org/D10764