More screenreader friendly Collapse, Take 2

This reverts 0ec05da0eea03849fc72bed84a2c7fe7be1de1b6 to bring back #14444, which fixes #14348 (again). I think I figured out all the kinks here now:

- Navbar contents are no longer hidden on desktop views  (missed that the last time around).
- Collapse demo works as expected.
- Tabs demo works as expected.

Does this screw with anything else? Am I missing any broken examples or components?

/cc @hnrch02 and @cvrebert for testing.