Change visibility type for panel hiding (#864)

* change visibility method for panels

* make the new visibility type opt in

src/sql/base/browser/ui/panel/media/panel.css

@@ -109,4 +109,8 @@ panel {
 .tabbedPanel > .title > .monaco-scrollable-element {
 	flex: 0 1 auto;
 	width: inherit;
-}
+}
+
+.visibility.hidden {
+	visibility: hidden;
+}