Make context drawer non-interactive
Reason for the change
The context drawer is interactive by default, which generates a column of dead pixels on the right side, per https://bugs.kde.org/show_bug.cgi?id=468211.
Since the issue hasn't been fixed upstream yet, let's disable interactivity in Elisa to work around it. We won't lose anything since nobody swipes from the side to show the drawer in Elisa, which has a dedicated mobile UI for small touch devices.
Test plan
Make the playlist scrollable and click and drag op and down and left and right on the right side of the playlist's scrollbar:
- Up and down: scrolls the view as you would expect
- Side to side: scrollbar continues to be held down; no context drawer opens