Rework Collapse component

[kaitmore]

The current Collapse component has a few issues around transitions and nested Collapses. See https://github.com/greymatter-io/gm-dashboard/issues/3693#issuecomment-725532805 for more details.

We want to rework the collapse component to not rely on calculating height for the transitions. The other requirement is that nested collapses should be a first-class use case, rather than an afterthought as it was with the original implementation.

Implementation ideas floated on slack by @shanberg

Stuart Hanberg 6:05 PM
I think we can avoid this type of problem by switching to a simpler animation method
6:06
which doesn’t require javascript and works with any height
6:06
just a slightly different style
Kait Moreno 6:06 PM
Yeah, that’s true. This approach feels very fragile.
Stuart Hanberg 6:08 PM
short story: use display none to hide, and play a CSS animation when shown, which quickly transitions opacity, scale, and some margin, to give a hint of expansion, without actually having to calculate anything