Avoid UI access in async viewers which operate on non UI threads #710

The AsynchronousViewer class hierarchy reuses the Viewer interface
but adds additional constraints on it, in particular it allows many
of its methods to be called from non-UI threads.

See javadoc summary:

https://github.com/eclipse-platform/eclipse.platform/blob/e92b72761b8543358ba9811ea49807f75e98bad5/debug/org.eclipse.debug.ui/ui/org/eclipse/debug/internal/ui/viewers/AsynchronousViewer.java#L57-L72

Commit 3b9c02c added UI access to method
that used to not have any, therefore this patch restores that non-UI
implementation locally consistent with other methods in the async viewer
that operate on the model.

Fixes #710

debug/org.eclipse.debug.ui/ui/org/eclipse/debug/internal/ui/viewers/AsynchronousViewer.java

@@ -414,6 +414,11 @@ protected Widget doFindInputItem(Object element) {
 	protected void doUpdateItem(Widget item, Object element, boolean fullMap) {
 	}
 
+	@Override
+	public void refresh() {
+		refresh(getRoot());
+	}
+
 	@Override
 	protected void internalRefresh(Object element) {
 		// get the nodes in the model