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
Use mesh batch cache for mesh selection.
Note that we could create the batches and free immediately
so they don't take up memory.
This resolves a problem where selection was limited
to immediate-mode buffer size.
These are intended for very simple drawing. No lighting etc.
Shares some fragment code with the 2D shaders.
Similar to their 2D counterparts, but are not combined because of
future plans for separate 2D & 3D matrix stacks.
