Think about a way to restrict WebGL2 to a minimal mode

In legacy/trac#16005 (moved) we made use of the miminal WebGL mode as a middle-ground for allowing WebGL while not being exposed to its fingerprinting capabilities.

Now that WebGL2 is available (see legacy/trac#16404 (moved)) we could think about doing something similar with the information exposed with it.

However, it is not sure whether that is a viable solution at all for at least two reasons:

1. There is no minimal mode in WebGL2 which would help us.
2. WebGL2 provides probably more powerful and resource-hungry features. Harmonizing them across older and newer computers while keeping them still usable might be tricky.