This PR updates the scrollbar diagnostic setting to provide fine-grained
control over which indicators to show, based on severity level. This
allows the user to hide lower-severity diagnostics that can otherwise
clutter the scrollbar (for example, unused or disabled code).
The options are set such that the existing boolean setting has the same
effect: when `true` all diagnostics are shown, and when `false` no
diagnostics are shown.
Closes#22296.
Release Notes:
- Added fine-grained control of scrollbar diagnostic indicators.
Aaron Feickert
f55a3629b0