Java FFI: support generic Java types in extern class foreign type

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: test generics in Java FFI

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
Merge: Java FFI with Java generics

To support extern classes of Java generic types, we remove all the parameters of generic types in the JNI signature format.

Example:

    extern class QueueOfString in "Java" `{ java.util.Queue<String> `}

Pull-Request: #572
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Frédéric Vachon <fredvac@gmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>