WebGPUSampler is much more complete than Dawn's Sampler.
This patch implement the missing part.
BUG=dawn:47
Change-Id: Ief45cb9710493e9d79ddab60fe3be5a123b76ebd
Reviewed-on: https://dawn-review.googlesource.com/c/3540
Commit-Queue: Shaobo Yan <shaobo.yan@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>