rbx_reflector is inconsistent with storing default values for properties about rbx-dom

[kennethloeffler]

This is happening because rbx_reflector is using DecodePropertyBehavior::IgnoreUnknown when deserializing the defaults place, so it will only apply defaults for properties that are already present rbx_xml's built-in database:

rbx-dom/rbx_reflector/src/defaults.rs

Lines 14 to 21 in 87d61fc

	pub fn apply_defaults(
	database: &mut ReflectionDatabase,
	defaults_place: &PathBuf,
	) -> anyhow::Result<()> {
	let file = BufReader::new(File::open(defaults_place).context("Could not find defaults place")?);
	let decode_options = rbx_xml::DecodeOptions::new()
	.property_behavior(rbx_xml::DecodePropertyBehavior::IgnoreUnknown);

This is not the desired behavior. We should be using DecodePropertyBehavior::NoReflection and then using the in-progress database (rather than the one in rbx_xml) to do reflection on the defaults place, similar to generate_reflection.