Instancing

[lilleyse]

Continuation of #3023 for issue #3001

I checked that instancing works the same on Edge and IE, as the vao extension isn't supported in either.

I added a test inside the Sandcastle dev folder. So far the performance results show that instancing and batching are typically equal for fps. Though instancing does offer some speed improvements when the billboards are constantly updating.

For test coverage, the instancing and batched code paths are very similar and even basic tests should cover most of the divergences. I did edit the non-instancing test to be slightly more robust. The code coverage for BillboardCollection is 98%.

I'll have the model instancing code up after these changes are reviewed.

[pjcozzi]

Though instancing does offer some speed improvements when the billboards are constantly updating.

What are the numbers? Are they significant?

Also, it may be hard to measure (check the GPU process), but did you observe a memory savings?

[pjcozzi]

Merging this into instancing-ready-for-master. Please open the model instancing PR into this branch too.