Check variable naming inside of getAttributeType and getPropertyType methods

[lukewarlow]

See WebKit/WebKit#26552 (comment) for context but TLDR make sure these two functions have parameters and variables named coherently.

[fred-wang]

So IIUC, the problem is the confusion with Element.tagName) which returns uppercased qualified name. So the suggestion is to rename the tagName parameter to use localName instead?

[fred-wang]

cc @smaug----

So another source of confusion is the "attribute" argument from getAttributeType().

Comparing with [createAttribute(https://dom.spec.whatwg.org/#dom-document-createattribute)] and createAttributeNS, it could better be renamed "local name" or "qualified name".

Besides lowercasing (see #424 for a proposal to remove that), the argument is pass as is to Get Trusted Type data for attribute which treats it as a "local name", so it seems what this attribute really is.