[foreign-memaccess] RFR 8224041: Name of layout classes should end with "Layout" suffix

[Maurizio Cimadamore]

Hi,
this is the last patch in the queue of Layout API cleanups, and, 
perhaps, the simplest one.

This patch simply adds a "Layout" suffix to all the nodes in the Layout 
hierarchy, to avoid over-general name such as 'Compound', 'Group', 'Value'.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/8224041/

Maurizio