Print Java-level method signatures in exception messages

[John Rose]

On Mar 19, 2019, at 6:33 AM, Lindenmaier, Goetz <goetz.lindenmaier at sap.com> wrote:
> 
> Exception messages thrown by the runtime contain method signatures
> in the JNI signature format.  This is not common to every Java developer.
> It would be preferable to print the signatures with Java types.

This would be a nice cleanup to our error reporting.

When reporting signatures, I suggest suppressing qualifiers
for readability.  That worked out well for MethodType::toString.

https://docs.oracle.com/javase/8/docs/api/java/lang/invoke/MethodType.html#toString--