<Swing Dev> RfR JDK-8076554, [macosx] Custom Swing text components need to allow standard accessibility

[Pete Brunet]

Please review the following patch.

Bug: https://bugs.openjdk.java.net/browse/JDK-8076554
Patch: http://cr.openjdk.java.net/~ptbrunet/JDK-8076554/webrev.02/

The problem is that the code is currently hardcoded to only support text
accessibility for JTextComponent using the DocumentListener,
CaretListener interfaces.  This eliminates the ability to provide
accessibility for a custom text components.  The resolution is to remove
the JTextComponent gate and use the PropertyChangeListener listener
interface with its ACCESSIBLE_CARET_PROPERTY and
ACCESSIBLE_TEXT_PROPERTY properties.

I tested this with the two test cases which can be found at
http://cr.openjdk.java.net/~ptbrunet/JDK-8076554/test/
running them side by side with VoiceOver.

Note that I will fix the similar JProgressBar and JSlider restrictions
in JDK-8154507 and JDK-8154508 respectively.

Pete