We need the ability to parse the GL version irrespective of
GL extension handling, so pull it out into its own class.
BUG=dawn:580
Change-Id: I620267146159ba8e4fa8cba5f6ebff57e981add0
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/33540
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Stephen White <senorblanco@chromium.org>