Use the separator as border between roomlist and main panel (#33598)

* Remove border from roomlist container

The separator will act as the border so we no longer need the roomlist
border.

* Use pointer events to detect click event

Otherwise the onClick handler would run when you resize the panel.

* Support showing the border in separator

* Update tests

* Disable double click behaviour on separator

* Fix screenshot tests failing

packages/playwright-common/src/fixtures/panel.ts

@@ -12,7 +12,7 @@ import { test as base } from "./services.js";
  * Rounding this number to a whole number would mean updating a whole
  * bunch of screenshots.
  */
-const LEFT_PANEL_WIDTH = "369.6875px";
+const LEFT_PANEL_WIDTH = "368.6875px";
 
 export const test = base.extend<{
     /**