No nice way to report a test_result::Errored

[RalfJung]

Some public functions like apply_custom return a Result<_, Errored>. However, it seems like there is no nice way to actually report such an error -- the fields a private, and the debug impl produces unreadable results.

Normal error reporting happens here:

ui_test/src/lib.rs

Lines 340 to 352 in 51c1edc

	for (
	status,
	Errored {
	command,
	errors,
	stderr,
	stdout,
	},
	) in &failures
	{
	let _guard = status.failed_test(command, stderr, stdout);
	failure_emitter.test_failure(status, errors);
	}

But this is not accessible to outside code.

Given that Errored is a public type, it'd be nice if there was also a publicly accessible way of reporting those errors. :)