Merge @foxglove/avl into avl

[jhurliman]

Here is a work in progress PR to merge https://github.com/foxglove/avl into this repo. There are a few important differences to review:

• The extensive unit tests have been replaced with a more succint set of tests. I think it would be nice to preserve the existing tests, but they would need to be ported to Typescript + Jest.
• The API has changed to only expose TS/JS primitives instead of internal node references. This avoids existing bugs in the library, but the change is debatable
• Support for duplicate keys has been removed. This was to simplify the implementation in @foxglove/avl which did not need to support duplicate keys, but it might be important to add that support back before merging upstream.
• Some methods with O(n) performance have been removed, and some additional query methods have been added