Updating OpenCloseTest to JUnit5

[vogella]

Adding jupiter API to MANIFEST.MF
Migrating OpenCloseTest to JUnit5

[vogella]

I assume that the build will fail as I now start to use JUnit5 for the first time in this plug-in @HeikoKlare please remind me what I have to do to make JUnit4 and JUnit5 co-exist.

[akurtakov]

Having the test suite JUnit 3.x parts (extends TestCase) being converted to JUnit 4.x first would be nicer as I'm not looking for a mixture of JUnit 3/4/5 in the same test bundle.

[github-actions]

Test Results

 1 818 files   -  3   1 818 suites   - 3   1h 33m 42s ⏱️ - 1m 35s
 7 724 tests  -  5   7 495 ✅  -  5  228 💤 ±0  1 ❌ ±0 
24 333 runs   - 15  23 583 ✅  - 15  749 💤 ±0  1 ❌ ±0 

For more details on these failures, see this check.

Results for commit 0f444ca. ± Comparison against base commit 4721af7.

This pull request removes 5 tests.

UiTestSuite org.eclipse.ui.tests.stress.OpenCloseTest ‑ testOpenCloseFile
UiTestSuite org.eclipse.ui.tests.stress.OpenCloseTest ‑ testOpenCloseIntro
UiTestSuite org.eclipse.ui.tests.stress.OpenCloseTest ‑ testOpenClosePerspective
UiTestSuite org.eclipse.ui.tests.stress.OpenCloseTest ‑ testOpenCloseView
UiTestSuite org.eclipse.ui.tests.stress.OpenCloseTest ‑ testOpenCloseWorkbenchWindow