[NTP] Add animations to shortcuts on layout change

Part 1 of 2.

Convert shortcuts from flexbox to absolute positioning. This allows us
to add animations to the shortcuts using transform.

This change adds the framework for future custom link animations and
adds animations for layout changes on window resize/zoom.

The old reorder logic is removed as well, and will be re-added in part
2.

Screencasts
LTR: https://drive.google.com/open?id=1mSpq__cnrmuJv0DDa3KhFv2iBCaFyguY
RTL: https://drive.google.com/open?id=1STJ5JZ7XV_k1g8AfbJm35GRTHmSsa-h7

Bug: 851335
Change-Id: Id63836e747a7c7dff4e25beaa1f082e7dc1f52e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1591954
Commit-Queue: Kristi Park <kristipark@chromium.org>
Reviewed-by: Kyle Milka <kmilka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657529}
8 files changed