[144] [omnibox][next] Enable/disable menu items based on current context.

Updates menu enablement state to properly enable/disable menu items
based on context. More explicitly:

1. Image generation should be possible only with one other image.

2. Deep research should not be possible when any other context is
atattched.

3. Adding more files than the max allowed number should not be allowed.

(cherry picked from commit 9eef7cca6baaef94a64766950f0b1353f7aefdce)

Bug: 462743439, 471210631
Change-Id: I1219d919739bc18215359373a0a2a14513804da7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7267684
Reviewed-by: Marlon Facey <mfacey@chromium.org>
Commit-Queue: Aviv Kiss <avivkiss@google.com>
Auto-Submit: Aviv Kiss <avivkiss@google.com>
Cr-Original-Commit-Position: refs/heads/main@{#1560308}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7310552
Reviewed-by: Krishna Govind <govind@chromium.org>
Commit-Queue: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/branch-heads/7559@{#2088}
Cr-Branched-From: 223dfbac1c7542a06b422390d954afe5b560b607-refs/heads/main@{#1552494}