This patch check FP16 support on vulkan backend, and introduces
the shader_float16 extension.
BUG=dawn:426
TEST=dawn_end2end_tests
Change-Id: Ie09568a416ce9eb2c11afeede3e7da520550d5fb
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/21901
Commit-Queue: Xinghua Cao <xinghua.cao@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jiawei Shao <jiawei.shao@intel.com>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
