Transitions and animations

[ZacSweers]

We have a few needs in this space! Currently, we offer some animation APIs via the backstack APIs, but let's try to flush this out into a full API.

• Inspired by @oldergod's mention in his Broadway talk at Droidcon NYC, let's explore implementing an AnimationFactory API to allow providing animations between two given screens. This would allow us to contribute a transition for these screens as keys.
• Batteries-included animations. We have one already where it defaults to CrossFade, let's make a few more available like PushLeft, PushRight, etc.
• Is the current backstack animation API good enough for our needs? Do we want to make other changes to better support an AnimationFactory API? What about looking at what https://github.com/rjrjr/compose-backstack does?

A good example for this would be to make the petlist -> detail transition use the iamge as a shared hero element

[ZacSweers]

Another option to consider: https://github.com/skydoves/Orbital

[ZacSweers]

Ran into this while using this in CatchUp, something to be mindful of: https://issuetracker.google.com/issues/266401829

[ZacSweers]

Someone sent me this as a good source of inspiration: https://medium.com/airbnb-engineering/motion-engineering-at-scale-5ffabfc878

[ZacSweers]

Another thing to keep an eye on: shared element transitions: https://android-review.googlesource.com/c/platform/frameworks/support/+/2499518