[cleanup] Eliminate doclint errors in javax/swing/text classes

Fix formatting errrors as reported by doclint doclet in javax/swing/text classes.
Piggybacked: javax/swing/JLayer.java, javax/swing/plaf/TextUI.java, javax/swing/plaf/basic/BasicTextUI.java.

This change should not be visible to the end user but should please the "javadoc -Xdoclint:all" compiler.