Remove some redundant GL validation.

[null77]

ANGLE itself can manage most of WebGL validation. This makes the transition to WebGL 2 validation easier because we won't need to write new logic for all the new entry points.

To this effect this enables robust memory features in ANGLE, and also updates the error set logic.

This contribution is funded by http://higharc.com/

@dhritzkiv this is the next functional change. Still passes all tests with the updated gl-conformance for me locally on Windows.

[null77]

Added a new push which removes some extra texture validation, helper functions, and validation in draw calls.

[null77]

Another small update with some extra validation removed for ANGLE_instanced_arrays.