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.

cherry-picked from commits d1462228 and
86a86a7d.

Bug: chromium:1088005
Change-Id: Ie4affc3f6f97789e9ea327272e308d19a609f19e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2810801Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>