AppMenu: Use PNG w/ shadow for low-end devices

Screenshots:
Light: https://screenshot.googleplex.com/9kmabPmrUXadeqo
Dark: https://screenshot.googleplex.com/BG4HaMeFTsMNiHH

Notes on testing dynamic colors:
- I did not add any automated tests for dynamic colors. Per
https://issues.chromium.org/issues/40786056, it seems like we don't
currently have the infrastructure to do this and are not interested in
putting in the effort at this point in time.
- I tested my code manually but it seems that dynamic "for me" colors
are not used in low-end device mode.

Fixed: 40818706
Test: AppMenuTest
Change-Id: I9ffd0f76e6140ea6cf3607de7174405feec3fc7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6227748
Reviewed-by: Neil Coronado <nemco@google.com>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Commit-Queue: Jenna Himawan <jhimawan@google.com>
Cr-Commit-Position: refs/heads/main@{#1417561}