Adding a Lightmapper (some progress) (Patreon)

As promised in the Patreon rewards, pledgers would see many previews and advances for new features first, it's just that we haven't been adding much recently given 3.0 is huge.

A large amount of users requested that an actual lightmapper is added to 3.0, given GIProbe requires relatively higher end hardware. It will be a rare last-minute addition, so here's some progress for it.

An UV unwrapper has been added that can generate unique UVs on the secondary channel on import automatically.

After this, work on a lightmapper will begin, should take a few days hopefully since it shares a lot of the code with GIProbe.