Write end-to-end test for scrolling component insert panel

Overview

The component insert panel displays a potentially long list of components to choose from and add to the content. We need to ensure that this list is scrollable in order to access all components.

Proposed resolution

Write an end-to-end test to make sure that the component insert panel is scrollable. With our canvas and preview logic where we listen to all kinds of mouse events, it's easy to introduce a bug that impacts scrollable areas. Let's make sure it doesn't happen anymore!

It's probably a good idea to test this in a standalone test case and stub the HTTP request which returns the list of components, so we can be sure we have enough components for the scroll to be necessary.