[ArcMigration: Lacros to ARC] Implement ArcObserver::OnIconInvalidated()

ArcMigration: Lacros to ARC aims to implement right-click and
smart selection handling for ARC apps in Lacros.

This CL implements ArcObserver::OnIconInvalidated.
By this change, Ash-chrome calls OnIconInvalidated and invalidate icons
in ArcIconCache in Lacros, but the cache is empty for now.

Also, this CL moves activity_icon_loader to components/arc/common/.
This directory is used for the file used from both ash and lacros.

This CL doesn't affect the behavior.

Bug: 1268687
Change-Id: I7598b642e51fbd19e98796874f2619369a5439fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3267821
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Maggie Cai <mxcai@chromium.org>
Commit-Queue: Eriko Kurimoto <elkurin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#945843}