Generalize ExpandableCard

[sproctor]

I thinking not passing the content into ExpandableCard is a big missed opportunity. This could easily be a library. I made these changes and a few others.

[Skyyo]

Hey, thanks for PR. With compose, so many things are easily achieved with small amount of code, that I'm not sure we need to create that many libraries these days.
We have Modifier.animateContentSize & AnimatedVisibility that allow us to do custom behaviour of expanding/collapsing.
I'd be surprised that people want to pull a library to do what they can do in few minutes of copy pasting, might be wrong though. We can discuss this @sproctor

[sproctor]

For me, I'd rather someone else worry about the specifics, particularly when there's an experimental component to it, but that's me. The result is good enough for my use. Thanks for providing a good example to work with. I think using the expanded variable directly instead of the transition state is a bug that the lint checker was rightfully indicating. This PR is turning a bit more into just what I would've done than something I'd necessarily expect to be pulled. My last commit is a simplification. It still works well, but maybe isn't how you would want things done. Use what you'd like from it.