... instead of RGBA32_FLOAT.  VK_FORMAT_R16G16B16A16_SFLOAT has
mandatory support for vertex buffers.

Bug: b/184163871
Change-Id: I7ef2933cd15e46bb984e6fd1b020d2ec15b9c60e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2807780
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>