RFR: JDK-8223914: specification of j.l.c.MethodTypeDesc::of should document better the exceptions thrown

[Vicente Romero]

Please review simple fix for [1] at [2] plus the CSR at [3]. This fix is 
simply documenting all the missing cases in which method 
java.lang.constant.MethodTypeDesc::of can throw exceptions. A test has 
been added to cover the missing cases.

Thanks,
Vicente

[1] https://bugs.openjdk.java.net/browse/JDK-8223914
[2] http://cr.openjdk.java.net/~vromero/8223914/webrev.00/
[3] https://bugs.openjdk.java.net/browse/JDK-8224136