… ops

It was possible to reuse WriteConcernError and WriteError with slight changes to their init functions.

This was not necessary for compilation, but it makes the header internally consistent.

Always return arrays for writeErrors and writeConcernErrors

…sults

Per CDRIVER-5843, libmongoc does not consistently populate this field. It also isn't required by the spec, so omit it for now.

Result maps should only be null if verboseResults=false. Additionally, the error reply document can default to an empty document on error (as it is in libmongoc).

Revise the stubs to reflect that executeBulkWriteCommand() always returns a BulkWriteCommandResult. If the result is unacknowledged, that is reported via isAcknowledged() and other methods can throw, which is consistent with WriteResult for the legacy bulk write API.

If the result is empty on error (i.e. no writes were successful), BulkWriteCommandException::$partialResult is left unset.

This also ensures that BulkWriteCommandException uses the original server-side error code and message (if available) for top-level errors.

mongoc_bulkwriteexception_errorreply() always returns an initialized document, but it may be empty. This ensures that an InvalidArgumentException is not unnecessarily proxied behind a BulkWriteCommandException.