snap-group: Add `cros.sys.inverse-whiteblack` color

This color is needed for the snap groups feedback button icon and
it's currently missing.

Fixed: b/328636970
Change-Id: Id696fc709c10bb4a4052951eb3b4b4869e9d08d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5353899


Commit-Queue: Michele Fan <michelefan@chromium.org>
Reviewed-by: Xiaodan Zhu <zxdan@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1269936}