Vulkan: merge client buffer data. some old fashion game still use lots of interleaved client buffer. instead of copy each attrib alone. this cl try to merge all the attrib ranges. reduce allocated memory and do whole range memcpy. Bug: b/306763053 Change-Id: I493d7f0e1ef593fb7059c36ae0ed2149c4595e42 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4960642 Commit-Queue: Hailin Zhang <hailinzhang@google.com> Reviewed-by: Charlie Lao <cclao@google.com>