Vulkan: Don't calculate vertex input state when dynamic When vertex input state is dynamic, VkGraphicsPipelineCreateInfo::pVertexInputeState can be nullptr. This change makes sure time is not wasted calculating this state at pipeline creation time. The change also ensures drivers don't rely on info provided at compile time by mistake. Bug: angleproject:42265637 Change-Id: I54da8be7769f0dd0767df6d7774baa956475bf8d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6510082 Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Charlie Lao <cclao@google.com>