[Phone Hub][Eche] Fix loading animation for more apps button

The PhoneHubMoreAppsButton's loading animation does not match the
"Skeleton Loaders" spec, so this CL fixes that by factoring out the
LoadingView's animation code into AppLoadingIcon and using it in both
places.

A "StopLoadingAnimation" method is also introduced, which will be
useful later to pause the animation before fading in the loaded view.

The size of the app icons / buttons has also been increased to 42px.
This brings us into spec, and makes the icons match the size of the
more apps button.

Screen capture:
https://drive.google.com/file/d/1vM3lbcRV4zm1-1tbhB-hf6Gku_twmUBd/view?usp=sharing&resourcekey=0-1gsylB4dHxAKV6VRqWgRNQ

TEST=Manual testing with the loading view forced on, manual testing
for regressions of the non-loading view.

Bug: b/271478560
Change-Id: I4704403c9c8ac047de560dec64c40cc54327b834
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4347745


Reviewed-by: Jon Mann <jonmann@chromium.org>
Commit-Queue: Curt Clemens <cclem@google.com>
Reviewed-by: Crisrael Lucero <crisrael@google.com>
Reviewed-by: Pu Shi <pushi@google.com>
Cr-Commit-Position: refs/heads/main@{#1118902}