Adding components to the canvas is hard

Overview

It is still really hard to build pages with XB because the drag and drop is inaccurate. Some of the numerous issues are:

1. Dragging items to the beginning and end is hard and the preview doesn't show accurately if the component will be dropped
2. It is really hard (impossible?) to drag components to some slots. For example CTA component from the Starshot Demo Design System.
3. The mouse position against the slots feels off (or there's delay?).

Proposed resolution

User interface changes