Add light mapping / AO baking demo

[gkjohnson]

UV Unwrapping

• Update, test UV Unwrapper on sample model using xatlas. UVUnwrapper, from Mozilla Spoke code

Lightmap Generation

1. Optionally generate a UV map
2. Adjust the path tracing shader to project into UV space rather than world space.
3. Flood the texture gaps (use mip maps?)
4. Apply to model

[Hoodgail]

When will this issue be closed and complete? 👀

[gkjohnson]

Depends on if and when someone wants to work on it. I have no plans to put time into this at the moment. But feel free to open a PR if you're interested in it to help it along and I can provide direction if needed.