LDrawLoader: Check if a face edge is a sub segment of a long edge when smoothing normals

[gkjohnson]

Related issue: #22957 (comment)

Description

This PR implements the approach mentioned in #22957 (comment) to create hard edges in the corner cases when a part is made up of multiple materials and edges stretch over multiple face edges that are broken up by color. It works by indexing every edge line as a normalized ray and then checking to see if face edges lie on that ray. This is more expensive but it is only run when if a part is made of 2 or more materials.

Before	After

In the Scorpion Pyramid model there are 55 parts total that are made of 2 or more materials and are therefore smoothed with this more advanced logic. Here's an image of those parts:

From doing some performance checks it doesn't look like this significantly impacts the performance of smoothing normals on the pieces where it's relevant.

A small side note that that red seat piece in the bottom left that looks like it is all one color is incorrectly formed and actually has one triangle that is a different material causing it to fall into the above condition. The most segments that have to be checked against once a face edge has been found to lie on an edge ray is 9 in the Scorpion Pyramid model.

cc @yomboprime

[yomboprime]

Amazing work. I've read the code, but honestly I can't make a deep review or tests at the moment.

[mrdoob]

Lets merge this for now.

[mrdoob]

Thanks!