[JDK9] RFR 8167229: Improve VarHandle documentation

[Paul Sandoz]

Hi,

Please review some documentation changes to VarHandle:

  http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8167229-varhandle-docs/webrev/index.html

There are no changes to the specification.

A significant portion of the changes are based on feedback from Alex who observed it’s possible to simplify the specification by removing the notion of shape and focusing on the list of coordinate types (the types of coordinate expressions).

Paul.