This commit brings MongoClientFactory and ReactiveMongoClientFactory
into functional alignment and reduces duplication in the classes
and their tests.

There are no behavior changes to ReactiveMongoClientFactory.
MongoClientFactory now throws an exception when a URI is configured
along with a host, port, or credentials, where it previousy ignored
host, port, and credentials silently. MongClientFactory now also
supports MongoClientSettingsBuilderCustomizers.

Fixes gh-20019