[webidl] Improve restrictions on attributes/operations when maplike/setlike are used (#49)

Two changes:

1)  Use of maplike/setlike should not affect static attributes/operations (but should affect constants, as it does now, since those go on the proto too).

2)  The mutator methods (clear, add, set, delete) should not be allowed to shadow a method on an inherited interface.  But having them on the interface itself or its consequential interfaces should be OK (as now) and just inhibit autogeneration of the method.

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Reply to this email directly or view it on GitHub:
https://github.com/heycam/webidl/issues/49