Additionally, makes the emulation path not require
independentResolveNone.  This was only used to select the NONE resolve
mode when the attachment format doesn't have either of depth or stencil
aspects, but it's ok to specify the same resolve mode for both aspects
even if one aspect is missing.

Bug: chromium:1088005
Change-Id: Ifc37cbf5331145179c5927853b996a0d62b871ee
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2743666Reviewed-by: David Reveman <reveman@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>