Investigate changes in NODE-4862: Remove internal constants from BSON public export

Use Case

As a node engineer
I want internal things to stay internal
So that I can reason about changes that cause major semver bumps

Acceptance Criteria

Implementation Requirements

• Remove the BSON constants from the public exports
• Add the BSONType enum from the driver to the BSON library

Testing Requirements

• Update exports unit test

Documentation Requirements

• Migration guide

Follow Up Requirements

• Make a note in the ticket that will have the driver adopt BSON v5 that it can remove its copy of the BSONType enum and re-export BSON's