<AWT Dev> 8167126: Create a module to provide access to non-SE desktop APIs

[Phil Race]

Webrev : http://cr.openjdk.java.net/~prr/8167126/

The upcoming jigsaw changes to limit use of setAccessible [1] mean
that some work-arounds for non-SE API users will be broken.
To provide for continued access to the capability (albeit via a
different package+class name) this fix adds a jdk.desktop module.
It may be that this is temporary - fixed with a standard API either
later in this release or in a subsequent release, but we need this
in place soon.

The proposed module name - as well as some details of this change -
have already been discussed with representatives of the jigsaw team.

-phil.