The bsonx package contains Doc, Arr, Elem, and Val types that are largely unused. These were a POC of a typesafe BSON API and were used extensively in the 1.0 driver, but the usages were replaced by bsoncore when we refactored our operations layer in v1.1. We should remove these types as they are no longer useful for us and, as far as we're aware, are not used by internal/external consumers.

Updated reduced scope:

• Remove all usages of "x/bsonx" API from the "production" driver code except where necessary to maintain backward compatibility with external usages of that package (e.g. in type switch statements).

The full scope is now captured in GODRIVER-2416.