Refine D3D9/D3D11 ANGLE heuristics

[lexaknyazev]

• It must be D3D11 for WebGL 2.0.
• Some configurations report non-power-of-two uniform vectors on D3D11 (e.g. 4095 on GTX 1060).

[pjcozzi]

Thanks @lexaknyazev, feel free to open a PR if you have the bandwidth. Just also send in a CLA, we use Cesium's - https://github.com/AnalyticalGraphicsInc/cesium/blob/master/CONTRIBUTING.md#contributor-license-agreement-cla

CC #38

[emackey]

@lexaknyazev @pjcozzi Just a quick update from Ken Russell on this. In a post to the WebGL mailing list, Ken writes:

... right now Chrome doesn't use ANGLE on Android. However, the team is switching to use ANGLE on all platforms, so it's a work-in-progress.

So it sounds like our ANGLE heuristics will be changing a lot soon.