Rename "_with_write_concern" functions (introduced in CDRIVER-1322) to "_with_opts", accept a const bson_t opts instead a mongoc_write_concern_t:

• mongoc_collection_aggregate_with_opts mongoc_collection_aggregate already has bson_t *options that be retrofitted
• mongoc_collection_create_index_with_opts
• mongoc_collection_drop_index_with_opts
• mongoc_collection_drop_with_opts
• mongoc_collection_rename_with_opts
• mongoc_database_create_collection_with_opts mongoc_database_create_collection already has bson_t *options that can be retrofitted
• mongoc_database_drop_with_opts

For consistency with the rest of our API, the final parameters of each of these functions should be ordered like:

   const bson_t *opts
   bson_error_t *error

Or:

   const bson_t *opts
   bson_t *reply
   bson_error_t *error

Their internal helper _mongoc_client_command_with_write_concern should become:

• _mongoc_client_command_with_opts

This function accepts a const bson_t "opts" instead of a mongoc_write_concern_t. Users can easily pass us a mongoc_write_concern_t in "opts" using mongoc_write_concern_append. The same rules currently enforced by _mongoc_client_command_with_write_concern MUST be enforced by the new _mongoc_client_command_with_opts:

• If "opts" has a "writeConcern" subdocument, append it to the command iff max wire version >= 5
• If "opts" has a "writeConcern" subdocument, parse the reply for "writeConcernError" and return false if there is a write concern error

Besides "writeConcern", I think other fields in "opts" are appended to the command without any validation.