Fix flapping tests by replacing fixed delays with condition-based waiting

[laeubi]

No description provided.

[github-actions]

Test Results

 3 018 files  +1 006   3 018 suites  +1 006   2h 5m 20s ⏱️ + 50m 1s
 8 234 tests ±    0   7 985 ✅ ±    0  243 💤  -   6  3 ❌ +3  3 🔥 +3 
23 622 runs  +7 874  22 828 ✅ +7 579  776 💤 +277  9 ❌ +9  9 🔥 +9 

For more details on these failures and errors, see this check.

Results for commit b07b2a8. ± Comparison against base commit 6f2025c.

This pull request removes 6 and adds 6 tests. Note that renamed tests count towards both.

org.eclipse.ui.tests.decorators.DecoratorTableTest ‑ testBackground
org.eclipse.ui.tests.decorators.DecoratorTableTest ‑ testFont
org.eclipse.ui.tests.decorators.DecoratorTableTest ‑ testForeground
org.eclipse.ui.tests.decorators.DecoratorTreeTest ‑ testBackground
org.eclipse.ui.tests.decorators.DecoratorTreeTest ‑ testFont
org.eclipse.ui.tests.decorators.DecoratorTreeTest ‑ testForeground

UiTestSuite DecoratorsTestSuite DecoratorTableTest ‑ testBackground
UiTestSuite DecoratorsTestSuite DecoratorTableTest ‑ testFont
UiTestSuite DecoratorsTestSuite DecoratorTableTest ‑ testForeground
UiTestSuite DecoratorsTestSuite DecoratorTreeTest ‑ testBackground
UiTestSuite DecoratorsTestSuite DecoratorTreeTest ‑ testFont
UiTestSuite DecoratorsTestSuite DecoratorTreeTest ‑ testForeground

♻️ This comment has been updated with latest results.