Umbrella issue for text layout optimization.

Investigation of RT-5001 has revealed that text-layout under JavaFX is much slower than under a pure Java app. I've attached a small suite of standalone test cases that demonstrate this. Results on my machine (Vista on a MBP) are as follows:

JTextLayout.java (pure Java/Swing): ~275fps
SwingTestLayout.fx (FX, embedded Swing: ~220fps
TextLayout.fx (pure FX using Text node): ~22fps

One cause for this has been found, RT-5069.

Some notes on running the tests:
* To get fps data for the FX version(s), you'll need:
    * to point -Djava.util.logging.config.file= to the attached logging.properties
        AND
    * a Soma build which includes the RT-4959 fix OR a Soma/Marina build w/ a diff similar to:
        http://jfxsrc.sfbay.sun.com/javafx/soma/scrum/graphics/runtime/rev/557f74ded7ac

* To get framerates > ~70 for the embedded Swing test (SwingTextLayout.fx), you'll need to increase the javafx framerate with something like:
      -Djavafx.animation.framerate=500