[context-input] Suppress lns_surface param when there is no image

This was causing user-uploaded PDF files to not return an AIM response
successfully.

Also, moves the feature flags that affect the query controller into a
shared struct to simplify changes to the interface in the future.

Bug: b:430070871
Change-Id: I42f8acb5253dad57d2ff5969bbe43a8cf789b0c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7038306
Reviewed-by: Ameur Hosni <ameurhosni@google.com>
Commit-Queue: Jason Hu <hujasonx@google.com>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1529566}