RFR: JDK-8247849: permits clause of sealed interfaces should not allow parameterized types

[Vicente Romero]

Please review fix for [1] at [2]. I forgot to check that the `permits` 
clause of interfaces can't list any parameterized type, which is already 
done for classes. Now I have extracted the common code for classes and 
interfaces, the one that takes care of the `permits` clause, to avoid 
this kind of issues in the future,

Thanks,
Vicente

[1] https://bugs.openjdk.java.net/browse/JDK-8247849
[2] http://cr.openjdk.java.net/~vromero/8247849/webrev.00/