[omnibox] Appends Lens response to multimodal sb typed Suggest requests

Given that updating the placeholders in prepopulated_engines.json needs
a version change and the initial placeholder name won't be true to the
meaning of this param (due to obfuscation), rather than introducing a
placeholder, this change simply appends this param to the final request
URL in RemoteSuggestionsService. In the future, it'll probably be
better to introduce a placeholder and do replacement like other standard
params.

This change is limited to SearchProvider only. ZeroSuggestProvider is
much more nuanced and needs to be done as a follow up CL.

Bug: b:328763711
Change-Id: I7ba4df6f8120210248fe0f53a844defefee335de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5426818


Reviewed-by: Jason Hu <hujasonx@google.com>
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283897}