Shortcut: Add nudge to show not match for search key shortcut

When a user presses a search key plus top row key and there's no
behavior matches, pop up a nudge to suggest using Fn key instead of
search key.

Screenshot: https://screenshot.googleplex.com/3ygDcC72ywSJAy8

Test: unit_tests
Bug: b/216049298
Change-Id: I4862f1da4aa486e866d171aaf2c52f708eef3eb8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5373063
Reviewed-by: Gavin Williams <gavinwill@chromium.org>
Commit-Queue: Yuhan Yang <yyhyyh@google.com>
Reviewed-by: David Padlipsky <dpad@google.com>
Reviewed-by: Kevin Radtke <kradtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1275323}