Show scrollbar in CollectionsDrawer as needed

[cosmic-snow]

Fixes #2573.

Describe your changes

Make the scrollbar visible (AsNeeded) when there are more collections to display than what fits the height.

Issue ticket number and link

• Missing LocalDocs Scrollbar #2573

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• I have added thorough documentation for my code.
• I have tagged PR with relevant project labels. I acknowledge that a PR without labels may be dismissed.
• If this PR addresses a bug, I have provided both a screenshot/video of the original bug and the working solution.

Demo

Before: see linked issue
After:

Steps to Reproduce

Have more collections than what fits in the right drawer in chat.

Notes

Maybe I'm missing something here, but there already was a ScrollView in place, just the scrollbar turned off for some reason.
So this might not be the proper way to address the issue.

[manyoso]

Hmm, I need to look at this. If you look at the ListView right below it ... it has a Scrollbar that I think should work.

[cosmic-snow]

Yes, please do. I was suprised to find a ScrollView already in place, but with the scrollbar turned off. The change works, but it feels like I'm missing something.

[cosmic-snow]

Oh weird. If I set anchors.left: listView.right - 20 in the ListView's scrollbar instead, then I get one. Although not where I expected it.

Edit: Maybe the intended way to do it was keeping the original AlwaysOff but setting the nested scrollbar to anchors.right: listView.right instead of anchors.left: listView.right?

I admit I don't really understand why it behaves the way it does.

[cosmic-snow]

How accurate is Qt across platforms? This looks fine for me now on Windows.

Screenshot of bottom right area, scrolled all the way down: