We should stop raising DeprecationWarning when no UuidRepresentation has been specified by the user.

Note that a similar warning will be added back to PyMongo 3.12 as part of PYTHON-2309 to aid users in transitioning from PyMongo 3.x to PyMongo 4.x.

Original Description

We should improve the uuidRepresentation deprecation warnings added in PYTHON-2152. For example, this should raise a warning but doesn’t:

>>> import bson
>>> bson.encode({'u': uuid.uuid4()})
b'\x1d\x00\x00\x00\x05u\x00\x10\x00\x00\x00\x03W\xbd\xdchssDr\x86\x1e\x07i\xe1\xa2\xc4B\x00'

Same for bson.decode(), and json_util.loads/dumps when encoding/decoding UUIDs with the default options.

Another area to improve is that creating a MongoClient seems to cause a warning to be created but it’s attributed to codec_options.py. It’ll be hard for users to diagnose this warning:

>>> c = MongoClient()
/Users/shane/git/mongo-python-driver/bson/codec_options.py:333: DeprecationWarning: Starting in PyMongo 4.0, the default uuidRepresentation will be changed to 'unspecified'. Applications will need to explicitly set 'uuidRepresentation=pythonLegacy' in the connection string to preserve current behavior.
  return CodecOptions(

Instead the DeprecationWarning should point to line where the MongoClient was created.