perf: speed up debug triangle rendering

[kylebarron]

Closes #42

• Create binary array of triangle positions instead of many small JS arrays
• Create binary array of colors
• Create binary array with earcut indices. Since we're starting with triangles, we shouldn't have to perform triangulation via algorithm.

Some element of this isn't quite right. I'll probably have to go into lonboard/deck.gl-geoarrow and log out the exact data format being passed into the upstream layers.