The separation between the bsontype and bson package will be unnecessary once all BSON library packages are merged together. Merge all code from the bsontype package into the bson package.

Definition of done:

• Copy all code from the bsontype package to the bson package.
• Rename the bsontype.Type constants to {Type*}} (should match the existing "type" constants currently in the bson package).
• Copy and un-export the Type constants from the bsontype package to the bsoncore package to avoid importing the bson package into bsoncore.