Blender Git Loki

Cleanup: PyBGL, Clang-Tidy readability-function-size fixes

This addresses warnings from Clang-Tidy's `readability-function-size`
rule in the `source/blender/python` module.

It's just `BPyInit_bgl()` that's been split up into one or two smaller
functions per OpenGL version.

No functional changes.