bindings: Supports inheritance of [Unforgeable] attributes as accessor-type properties.

Source/core/dom/XMLDocument.idl

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 // https://dom.spec.whatwg.org/#xmldocument
 
 interface XMLDocument : Document {
-    // Inheritance of [Unforgeable] attributes is not supported.  So we have to
-    // define the same unforgeable attributes in derived interfaces as well.
-    // See that Document already defined 'location' attribute and this interface
-    // redefine it.
-    // Keep all the definitions consistent.
-    // TODO(yukishiino): Support inheritance of attributes defined on instance.
-    [PutForwards=href, Unforgeable] readonly attribute Location? location;
 };