desk_templates: Add inactive tabs to the DesksTemplatesIconContainer

When the DesksTemplatesIconContainer was first implemented, it only
considered the favicons of active tabs for it for the sake of
simplicity. Ideally, the DesksTemplatesIconContainer would display the
favicons of inactive tabs as well.

This CL makes it so the favicons of inactive tabs can also be added to
the DesksTemplatesIconContainer as well.

Test: Added
Bug: 1247777
Change-Id: I686d13fb11cbe9af2a4616b7df83d018fc024a18
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3298492
Commit-Queue: Jeremy Chinsen <chinsenj@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#945973}