Make scrollbars auto-hide by default (#38340)

With this, scrollbars across the app will now auto-hide unless it is
specified that they should follow a specific setting.

Optimally, we would just track the user preference by default. However,
this is currently not possible. because the setting we would need to
read lives in `editor` and we cannot read that from within the `ui`
crate.

Release Notes:

- N/A
fb60f710e3Finn Evers committed on 9/18/2025, 3:08:14 PM· committed by GitHubparent589e2c0
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