Add help buttons to extension settings

[FliegendeWurst]

Purpose of this PR: make it easier to find the KeY docs. The help buttons seen below lead to the docs / the extension's readme.

TODO: write a one-line description for each extension

Other changes:

• fixed the BROWSE action on Linux (see SwingUtil)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (8b189b1) 37.86% compared to head (f15831c) 37.86%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3348 +/- ## ========================================= Coverage 37.86% 37.86% Complexity 16904 16904 ========================================= Files 2055 2055 Lines 125528 125528 Branches 21226 21226 ========================================= Hits 47525 47525 Misses 72152 72152 Partials 5851 5851 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.