[omnibox][toolbelt] Use only verbatim user input when clicking action

Before, the currently entered text would carry over into keyword mode.
This could be inline autocompleted text or some keyboard-selected
match text. After this CL (conditioned on a new feature parameter,
SelectToolbeltBeforeOpening), any text directly entered by the user
will be used instead because this is the fill_into_edit for the
toolbelt match. Selecting the toolbelt consistently can avoid
potential unexpected gotchas as discovered in the bugbash.

Bug: 430633130
Change-Id: I0dcb37a22bc353793354e71e3816a91f17df5f13
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6720193
Reviewed-by: Khalid Peer <khalidpeer@chromium.org>
Reviewed-by: Orin Jaworski <orinj@chromium.org>
Commit-Queue: Orin Jaworski <orinj@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1485277}