Request for approval to backport: JDK-8133917 X11FontManager refactor

[Roman Kennke]

This is a backport of:

http://bugs.java.com/bugdatabase/view_bug.do?bug_id=8072436

It refactors X11FontManager such that the fontconfig specific parts go
into its own superclass FcFontManager. It's needed for Caciocavallo,
and probably useful for any non-X11 implementation that still wants to
use fontconfig.

The backport request is:
https://bugs.openjdk.java.net/browse/JDK-8133917

The actual backport is:
http://cr.openjdk.java.net/~rkennke/refactor-x11fm/webrev-jdk8u.00/

It is exactly the same change that has been applied to JDK9 and lived
there for a while, except modules source path changes:
http://cr.openjdk.java.net/~rkennke/refactor-x11fm/webrev.02/

Best regards,
Roman