Because of the platform refactor in abf38572 we broke the way
the tests override the D3D workarounds for the tiny depth/stencil bug.

This change passes a pointer to the platform directly in the EGL init
logic, which solves this issue. It also removes all decltype code in
the platform header which might fix the UBSAN problem we were seeing
previously.

Also change a present mode selection error into a warning in the Vk
back-end, since this was being triggered on AMD, but is safe.

BUG=angleproject:2042

Change-Id: Ibbd0c69ce11a840cf4b33c616f56020001e553aa
Reviewed-on: https://chromium-review.googlesource.com/513519Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>