Optimize picking primitive generation

[tsherif]

Significant optimizations to the the generation of picking primitives for ray picking. In the new performance example provided, time to generate picking primitives was reduced from ~380ms to ~60ms. Memory churn is also reduced due to picking geometry arrays being pre-allocated, and overall memory footprint is reduced because picking primitives no longer need an index array.

Also fixes a bug that prevented picking from working with meshes containing more than 64k vertices.

Key changes include:

• Use drawArrays to draw picking primitives, so indices are no longer needed.
• Pre-allocate arrays for picking positions and colors rather than pushing to dynamic arrays.
• Don't re-allocate arrays when creating WebGL buffers.
• Get picking positions and colors in a single pass, if possible.
• Example of ray picking on an extremely large mesh (1.28M triangles).

[tsherif]

@xeolabs I'm curious to know if this helps with the issues you were seeing on your phone.

[xeolabs]

Deployed, thanks.