Update Swing LaF in the AWT event dispatcher thread

[ptziegler]

Updating the LookAndFeel within the SWT UI thread may lead to a deadlock when using e.g. the GTKLookAndFeel. The update should be done asynchronously do avoid both treads blocking one another.

[ptziegler]

See https://github.com/eclipse-windowbuilder/windowbuilder/actions/runs/24117437192/job/70364204873. The LookAndFeelTest shouldn't use the OSSupportLinux and apparently only gets stuck on Java 24. So I don't think this is causing the problem. I think the most likely explanation is that the interaction between SWT and Swing doesn't work that well in this specific version.

[github-actions]

Test Results

 2 720 files  +  170   2 720 suites  +170   12h 38m 51s ⏱️ + 1h 10m 51s
 7 018 tests ±    0   6 960 ✅ +    1   58 💤 ± 0  0 ❌ ±0 
28 072 runs  +1 240  27 830 ✅ +1 217  242 💤 +24  0 ❌ ±0 

Results for commit ed5b4db. ± Comparison against base commit 682778f.