GL: Add disableRenderSnorm workaround Disable the extension on Mesa versions that clamp negative snorm values to zero on read. Fixed: angleproject:8315 Change-Id: I5459db40cb08c546fba15f5e6d70578029a8218a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4804324 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>