stabilize more of collections

This stabilizes most of libcollections, carefully avoiding sections of API which are being managed in other PRs. APIs which are not stable are marked explicitly unstable with a reason. Also deprecates the following:

* DList
  * rotate_forward
  * rotate_backward
  * prepend
  * insert_when
  * insert_ordered
  * merge

* VecMap
  * update
  * update_with_key

as such this is a

[breaking-change]
I may have lost track of these over time, but just wanted to confirm that we don't want to implement these for the `BTreeSet` value types? That would allow lifting the `Clone` bound and pushing the cloning up to users of the API.