RFR 8246095: Tweaks to memory access API

[Maurizio Cimadamore]

Hi,
this followup change includes a number of tweaks that have been added to 
the memory access API while we were in the process of integrating it. 
Most of them have been contributed by Chris (thanks!), and are all 
listed in great details in the CSR below:

https://bugs.openjdk.java.net/browse/JDK-8246096

Implementation-wise it should be all relatively straightforward - apart 
for the bit of surgery on lambda forms which was required to add a new 
kind of lambda forms to 'collect' return values. For now this method 
handle adaptation is package private, and can only be used by 
MemoryHandles::filterValues - but, if people find it useful, we might 
consider adding it to the MethodHandle standard combinator toolbox.

Cheers
Maurizio


Webrev:

http://cr.openjdk.java.net/~mcimadamore/8246095_v1/webrev/

Javadoc:

http://cr.openjdk.java.net/~mcimadamore/8246095_v1/javadoc/jdk/incubator/foreign/package-summary.html

Specdiff:

http://cr.openjdk.java.net/~mcimadamore/8246095_v1/specdiff/overview-summary.html