The Loop’s algorithm for mesh subdivide.

## 🚀 Feature

Subdivide mesh using Loop’s algorithm[1], similar to [open3d.geometry.subdivide_loop](http://www.open3d.org/docs/0.7.0/python_api/open3d.geometry.subdivide_loop.html).

[1] Loop, “Smooth subdivision surfaces based on triangles”, 1987

Start by comparing the requested behavior with open3d.geometry.subdivide_loop and read Loop’s “Smooth subdivision surfaces based on triangles” paper. Determine the project entry point and tests for mesh subdivision, then verify that triangular meshes are subdivided with the expected Loop geometry and topology.

Written by the indexing model from the issue text.