refine geosphere based on octahedron instead of icosahedron

Creating a geosphere based on octahedron allows for more usable uv generation (e.g. for equirectangular maps). Implementation is discussed and illustrated here: https://www.binpress.com/creating-octahedron-sphere-unity/
* create octahedron.ts
* refine icosahedron and octahedron w.r.t. latest webgl-operate naming conventions

Start by reading the linked octahedron-sphere implementation and inspecting the existing icosahedron code, then identify where the latest webgl-operate naming conventions apply. Create octahedron.ts and refine both sphere implementations; done means the octahedron-based geosphere exists with UV generation suitable for equirectangular maps and the naming is consistent.

Written by the indexing model from the issue text.