To test that the options are getting passed through correctly to the C driver, the C++ driver implements tests that "interpose" between the C driver's database calls and assert that the options are what they're supposed to be. In order to implement CXX-771 (https://jira.mongodb.org/browse/CXX-771), we need access to the `max_time_ms` field of `mongoc_find_and_modify_opts_t`, which currently is not public, and access to the other fields would help us more fully test the functionality of the `find_one_and_modify` calls. The implementation of this could either be making "getter" functions for the fields or just making the struct's implementation public rather than defined in a private header.