EXT_debug_utils is a (relatively) new extension that subsumes
EXT_debug_report and EXT_debug_marker extensions.

This change uses EXT_debut_utils (if available) to receive debug
messages, keeping EXT_debug_report as fallback.

Bug: angleproject:2798
Change-Id: Ia6767604548704e18f8150a54d2533c0b1197841
Reviewed-on: https://chromium-review.googlesource.com/c/1403955
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>