Instead of duplicating the initialization of every field, use one of the
constructors to initialize the other ones.

Bug: angleproject:3569
Change-Id: Ie342111218235ecb4124deb2f0147f97cdbed51a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1972889Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>