Fix time input AM/PM toggle

In a time input, fast toggling between AM and PM using the `a` and
`p` keys doesn't work because TypeAhead considers the fast typing of
keys as part of the same session. Since the AM/PM field has only 2
options, the TypeAhead session should be reset to enable fast
toggling between them.

Bug: 41429476
Change-Id: Ic3f401c7ae0831779ecae09bee58172bd8875d7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5618175
Commit-Queue: Traian Captan <tcaptan@chromium.org>
Reviewed-by: Mason Freed <masonf@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1314111}