web-sys: Use mixins instead of [NoInterfaceObject] interfaces and implements

I think these might all be from before WebIDL mixins existed. Either way,
multiple inheritance of interfaces that don't have exposed interface objects is
equivalent to mixins.

crates/web-sys/webidls/enabled/Text.webidl

@@ -23,4 +23,4 @@ partial interface Text {
   readonly attribute HTMLSlotElement? assignedSlot;
 };
 
-Text implements GeometryUtils;
+Text includes GeometryUtils;