Convert RGB/RGBA/SWT tests to JUnit 5.

[akurtakov]

Shorter tests, better reports of problems, more idiomatic JUnit usage.

[github-actions]

Test Results

   541 files  + 6     541 suites  +6   32m 42s ⏱️ + 1m 10s
 4 363 tests +36   4 347 ✅ +33   16 💤 +4  0 ❌  - 1 
16 592 runs  +33  16 478 ✅ +27  114 💤 +7  0 ❌  - 1 

Results for commit b079f02. ± Comparison against base commit 0b7090f.

This pull request removes 1 and adds 37 tests. Note that renamed tests count towards both.

org.eclipse.swt.tests.junit.Test_org_eclipse_swt_SWT ‑ test_Constructor

AllWin32Tests org.eclipse.swt.graphics.ImageWin32Tests ‑ testImageDataForDifferentFractionalZoomsShouldBeDifferent
AllWin32Tests org.eclipse.swt.graphics.ImageWin32Tests ‑ testImageShouldHaveDimesionAsPerZoomLevel
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testByteArrayTransfer
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testFileTransfer
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testHtmlTransfer
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testImageTransfer_fromCopiedImage
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testImageTransfer_fromImage
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testImageTransfer_fromImageData
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testImageTransfer_fromImageDataFromImage
AllWin32Tests org.eclipse.swt.tests.win32.Test_org_eclipse_swt_dnd_DND ‑ testRtfTransfer
…

This pull request skips 1 test.

org.eclipse.swt.tests.junit.Test_org_eclipse_swt_SWT ‑ test_isLocal

♻️ This comment has been updated with latest results.