JAVA-1394: Move Document and related classes from driver-core to bson

This is all automated refactoring.  I moved Document from org.mongodb to org.bson.types to that it's along side existing classes like Binary and ObjectId.  I moved the related codecs from com.mongodb.codecs to org.bson.codecs.

This class is a copy of the one from driver-core so I'm leaving it in for future use in the bson module even though it's currently unused.  I didn't want driver-core reaching into bson for its Assertions, which is why I copied it.