Vulkan: Clear depth and stencil unresolve separately To take into account two situations. 1. LoadOp for depth and stencil attachments are set differently. 2. depth and stencil unresolves could be different between the previous render pass and the current render pass. Bug: angleproject:42266019 Change-Id: I9e069b3972f86abb84eee6280919e6bba2901225 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6590197 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>