This uses the EGL_ANGLE_feature_control extension through the test
harness to control feature selection via a test config. This obviates
the need for the hacky platform methods table override.

Also adds a command graph feature that will be used to prototype the
command graph linearization for Vulkan.

Bug: angleproject:4029
Change-Id: Id37fadd5d2c317c9d9dd90dfab1fdc8e4ac3701f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2007612
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>