Reland "Animate side panel opening and closing."

This is a reland of commit 7b94b89e

See patchset 1 vs 2 for the change. The waiter for the extension's
container side panel close button only monitored the button visibility
when it should have been monitoring the container's visibility as well.

Original change's description:
> Animate side panel opening and closing.
>
> Create an animation that slides the side panel out from the side of the
> browser. This updates the side panel and side panel coordinator to use
> an enum, SidePanelContentState, to convey when a view should be hidden
> and allow us to delay hiding it until the side panel has been closed.
>
> Bug: 328295071
> Change-Id: I40b099a1a3d0469ba815caf152fb0ecc3562af2f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5406892


> Commit-Queue: Caroline Rising <corising@chromium.org>
> Reviewed-by: David Pennington <dpenning@chromium.org>
> Reviewed-by: Eshwar Stalin <estalin@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1280923}

Bug: 328295071
Change-Id: I64ecc52f74ade357ad8543cce98ff6daa4949c2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5415398


Auto-Submit: Caroline Rising <corising@chromium.org>
Reviewed-by: David Pennington <dpenning@chromium.org>
Reviewed-by: Eshwar Stalin <estalin@chromium.org>
Commit-Queue: David Pennington <dpenning@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1281605}