The GN arg angle_expose_non_conformant_extensions_and_versions is being
added to control exposeNonConformantExtensionsAndVersions, which enables
non-conformant features and extensions. In particular, this is being
done to enable EXT_texture_buffer on devices that don't support all of
the necessary formats since many Android games rely on this extension,
such as "Special Forces Group 2", "Fortnite", and "PUBG".

  # Enables non-conformant extensions and features
  angle_expose_non_conformant_extensions_and_versions = false

Users/vendors can now toggle the value with a GN arg, rather than a code
change, to make it easier to test the conformant version of ANGLE with
CTS, dEQP, etc. and/or app-compatibility.

Bug: angleproject:5592
Change-Id: Icbf18b48a2751c03e277ae964e1ec278a43324cf
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2740643Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Tim Van Patten <timvp@google.com>