Vulkan: add feature control for client buffer merge add feature control for client attribute buffer merge. default is off to reduce memeory usage for some application. Bug: b/328301788 Change-Id: I5bfd39fb1ea656ebb29bd2dc21726b60bbc1a8d2 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5410942 Commit-Queue: Hailin Zhang <hailinzhang@google.com> Reviewed-by: Charlie Lao <cclao@google.com> Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com>