a11y: treeview get current entry focused

This hack removes the need to press the `tab` key in order to get a tree entry
focused after clicking on it.

That improves usability for the Navigation pane and also for gridview such as
the one for the 'font' tab in the Format cell dialog.

Signed-off-by: Marco Cecchetti <marco.cecchetti@collabora.com>
Change-Id: I1be820367f935c8460ab5a60ef74cc648230ac64

browser/src/control/jsdialog/Widget.TreeView.ts

@@ -762,6 +762,7 @@ class TreeViewControl {
 		L.DomUtil.addClass(span, 'selected');
 		span.setAttribute('aria-selected', 'true');
 		span.tabIndex = 0;
+		span.focus();
 		if (checkbox) checkbox.removeAttribute('tabindex');
 	}