[Win] [Accessibility, Dialogs] Alert Dialog content is not fully read by Screen Reader

Summary

Add a new AccessibleRole called DIALOG for JavaFX Dialog windows.

Problem

None of the accessibility client application can read the content of a JavaFX dialog, because accessibility is not implemented for JavaFX Dialogs.

Solution

Implement accessibility for JavaFX Dialogs and add a new AccessibleRole called DIALOG.

Specification

javafx.scene.AccessibleRole

+
+    /**
+     * Dialog role.
+     * <p>
+     * Attributes:
+     * <ul>
+     * <li> {@link AccessibleAttribute#TEXT} </li>
+     * <li> {@link AccessibleAttribute#ROLE_DESCRIPTION} </li>
+     * <li> {@link AccessibleAttribute#CHILDREN} </li>
+     * </ul>
+     *
+     * @since 20
+     */
+    DIALOG