Vulkan: Skip load if depth/stencil value are undefined EGL1.5 spec says depth/stencil data are undefined after swap. This CL will track the depth/stencil data and mark it as undefined and skip the load if it is undefined. Bug: b/153885625 Change-Id: Ifb3d88d442da547fa78c1eae091cbae08a20d0ab Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2148179 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Charlie Lao <cclao@google.com>