Picker: Update units and maths icon in zero state.

Bug: b/329719529
Change-Id: I350f02c42a1c41e60e041794cee94f69195efd4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5422688


Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Auto-Submit: Patti Lor <patricialor@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282607}