Made the shading mode branches compile time instead of runtime in the renderer with templates

Did the same template if constexpr (compile time if branches) thing that we already do for opaque/transparent models with the shading mode (was a runtime per triangle if branch before), which improved performance. It basically just makes a new copy of the function for each shading mode x each transparency mode, so 4x2 which is 8 slightly different functions and uses the correct one on each call. That increases binary size and icache pressure, but drops per triangle or per pixel if branches that hurt performance, so it’s an overall performance win. Benchmarked across a ton of different resolutions, models, shading modes, etc. (the benchmark by itself took like 2 hours to run)