Vulkan: Fix loading instance extension entry points This change makes sure instance extension entry points are loaded right after the instance is. Previously, this was done after all features are initialized, including device features, but the code that decides the device features was using the instance entry points. Bug: angleproject:7959 Change-Id: I6869f40261eec7a3146c9e0e05b3fc139bc9223a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4247097 Commit-Queue: Ian Elliott <ianelliott@google.com> Auto-Submit: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Ian Elliott <ianelliott@google.com>