Rename Root<T> to DomRoot<T>

In a later PR, DomRoot<T> will become a type alias of Root<Dom<T>>,
where Root<T> will be able to handle all the things that need to be
rooted that have a stable traceable address that doesn't move for the
whole lifetime of the root. Stay tuned.

components/script/dom/bindings/codegen/Configuration.py

@@ -212,7 +212,7 @@ class Descriptor(DescriptorProvider):
             self.argumentType = "???"
             self.nativeType = ty
         else:
-            self.returnType = "Root<%s>" % typeName
+            self.returnType = "DomRoot<%s>" % typeName
             self.argumentType = "&%s" % typeName
             self.nativeType = "*const %s" % typeName
             if self.interface.isIteratorInterface():