[foreign] RFR 8217164: Enable jextract to handle function types in parameters

[Jorn Vernee]

Hi,

Please review the following patch which allows jextract to handle 
function signatures with simple function types as parameter types e.g.:

     void func(void callback(int)) { // function taking a pointer to 
function taking an int
         // ...
     }

Bug: https://bugs.openjdk.java.net/browse/JDK-8217164
Webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/8217164/webrev.00/

Thanks,
Jorn