Apply clang format as proposed in T53211.
For details on usage and instructions for migrating branches
without conflicts, see:
https://wiki.blender.org/wiki/Tools/ClangFormat
Some users of the 3D versions were storing 2D data in it.
Using a 3D tree for 2D data adds a spatially redundant branch
every 3rd level, as well as some extra memory use, best avoid this.