Add webgl2 support.

[rsturgell]

https://www.khronos.org/registry/webgl/specs/latest/2.0/

At a minimum we should alert the user that we don't yet support webgl2 if webgl recording is enabled and we see a getContext({experimental-}webgl2).

[sistr22]

+1 I have to say I was expecting the tool to work with webgl2 :/

[martin19]

+1