JBR-8646 add keyRelease invocations for pressed keys

Author: vprovodin

test/jdk/javax/swing/JSlider/bug4382876.java

@@ -76,6 +76,7 @@ public static void main(String[] args) throws Exception {
                     upFail = true;
                 }
             });
+            r.keyRelease(KeyEvent.VK_PAGE_UP);
             if (upFail) {
                 writeFailImage();
                 throw new RuntimeException("Slider value did NOT change with PAGE_UP");
@@ -87,6 +88,7 @@ public static void main(String[] args) throws Exception {
                     downFail = true;
                 }
             });
+            r.keyRelease(KeyEvent.VK_PAGE_DOWN);
             if (downFail) {
                 writeFailImage();
                 throw new RuntimeException("Slider value did NOT change with PAGE_DOWN");