Add scrollbar to panel manager

[dseguin]

Summary

None

Purpose of change

Fixes #54532.
The list of widgets in the panel manager is getting long enough to overflow the available drawing space.

Describe the solution

Add a scrollbar to the panel list. This is complicated by 2 things:

1. The panel manager is drawn as a single window, with the elements not necessarily grouped together.
2. The player can select and move a panel up and down the list, which relies on offsetting the other panels.

2022-01-18.16-38-25.mp4

TODO:

• Refactor the panel manager window into 3 separate windows
• Add a scrollbar to the left panel list
• Make the offsets follow the drawn portion when moving a panel
• Testing

Describe alternatives you've considered

Lengthening the panel manager window? The linked issue already explained why that's not a sustainable solution.

Testing

(See video above)

1. Added many new layouts to the custom sidebar config.
2. Open the panel manager and scroll up and down.
3. Press Enter to start moving a panel and scroll up and down.
4. Swap between lists with Right/Left.
5. Pressing Tab enables/disables the correct widgets/panels anywhere in the list
6. Switching sidebars still works the same.

Additional context

I thought it would be easy just to slap on a scrollbar, turns out it's a bit more complex :P

[PatrikLundell]

Do you need to handle the case that a sidebar name wraps around (in which case number of items can be less than number of lines), or does it get truncated when getting too long to fit in the panel?

[dseguin]

Do you need to handle the case that a sidebar name wraps around (in which case number of items can be less than number of lines), or does it get truncated when getting too long to fit in the panel?

If by that you mean making the window width dynamic to fit the text, then probably not. I can truncate the text with an ellipsis, sort of like how widgets handle it. Currently the text is cut-off if it's too long.

[PatrikLundell]

The problem I was asking about was if the text was wrapped around when the description wouldn't fit, as that complicates the scrollbar handling.
If "Silly widget with a really stupid name that does even more stupid things" was to be displayed as something like
"Silly widget with a really stupid name"
"that does even more stupid things"
the scrollbar would have to account for multi line entries, not just the fixed text at the top. I've encountered that problem in the past, and I think someone else is currently dealing with that kind of issue, which is why I asked. Truncation and ellipses both avoid this problem, so you should be safe from that.

[wapcaplet]

Works great!