Check CesiumJS against Mozilla's WebGL best practices

Mozilla (with the rest of the community) recently published a new version of the [WebGL Best Practices](https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API/WebGL_best_practices) document. We should comb through this and ensure CesiumJS follows it (except where it has a good reason not to of course).

For example, one piece of advice that immediately jumps out at me is to use `requestPostAnimationFrame` instead of `requestAnimationFrame`.

Start by reading Mozilla's WebGL Best Practices document and then inspect CesiumJS uses of requestAnimationFrame, including whether requestPostAnimationFrame is applicable. Review each recommendation against the current implementation, make justified changes where needed, and record exceptions where CesiumJS has a good reason not to follow the guidance.

Written by the indexing model from the issue text.