[foreign] RFR: do not infer layout from Java signatures

[Maurizio Cimadamore]

Hi,
as part of the cleanup I pushed yesterday, I realized there are quite 
few places where the binder infers layouts from the Java signatures 
rather than sticking to what the annotations say. This patch fixes such 
bad usages.

http://cr.openjdk.java.net/~mcimadamore/panama/dont-infer-layout-v2/src/java.base/share/classes/jdk/internal/nicl/Util.java.udiff.html

The only place where we need to do something like this is with variadic 
calls; so Util still has a function that goes from Class to Layout, but 
its scope is much more limited, and the resulting layout is also 
approximate (I've added comments in that direction), since varargs are 
always passed in register-aligned slots, regardless of the underlying 
real layout - so we don't need much 'inference' there.

I fixed a test which was missing layout annotation in a Java callback.

Maurizio