javadoc warning on Text::tabSizeProperty method

The new tabSize property in Text.java causes a javadoc warning during the build.

To reproduce this, run:

$ gradle javadoc

> Task :javadoc
/localhome/kcr/javafx/jfx-clean/jfx/rt/modules/javafx.graphics/src/main/java/javafx/scene/text/Text.java:1280: warning: no @return
    public final IntegerProperty tabSizeProperty() {
                                 ^
1 warning

The simple fix is to add:

* @return the property

One could argue that the doclet shouldn't give this warning, since it ignores anything you put in the @return anyway, but it's easier to add it to suppress the warning. I note that TextFlow doesn't have this problem because of the private field between the javadoc header and the property method.