The stream builder is difficult to use when it is mutated across multiple statements, and we would like to issue enable warnings when it is used in an unsafe manner (CXX-1152). To address mongocxx's current non-compliant uses of the stream builder (necessary in order to enable these warnings) and to set a good example for users, we should just replace its use of the stream builder with the basic builder, using the recently-added make_document() and make_array() helpers where appropriate.