getAttributeType and getPropertyType should default to HTML namespace, not ""

[smaug----]

Currently the algorithms oddly change empty string to HTML namespace. That prevents using the methods with elements which are in "" namespace (whether or not that is actual useful). But if the methods just defaulted to HTML namespace, then one could still explicitly pass "".

Even better would be to remove both methods, since it is unclear if they are needed.

[koto]

+1 to removing them, after confirming they see no significant enough usage.

[lukewarlow]

Based on discussion in #384 these potentially aren't going to be removed so it would be good to get clarification on the original question

[fred-wang]

This report was about elementNs.

getAttributeType() also has a attrNs param defaulting to the empty string and interpreting the empty string as null. I wonder whether we should do like https://dom.spec.whatwg.org/#dom-element-getattributens and change the IDL to use null as the default value. That won't change the behavior.

[annevk]

I think we should either make both namespace arguments optional or neither.