[foreign-abi] RFR 8237356: Refactor shared code in CallArranger

[Jorn Vernee]

Hi,

Please review the following patch which factors out some duplicated code 
in the different CallArranger implementations, most notably the code 
dealing with adapting MethodHandles for in memory return, but also 
splits out the binding generation code into different methods (which can 
now be tested separately [1]).

Bug : https://bugs.openjdk.java.net/browse/JDK-8237356
Webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/8237356/webrev.00/

I've also turned some of the assertions into if + throw, since we need 
to bail out always if these checks don't pass (and not just when 
assertions are enabled).

I've tested the Windows and Linux (WSL) implementations already, but not 
Aarch64.

Thanks,
Jorn

[1] : https://bugs.openjdk.java.net/browse/JDK-8237360