Improve Clipboard tests

[jonahgraham]

As I prepare my final Clipboard PR for #2126 I split out this test simplification and refactor to ensure that the tests still work as expected before my Clipboard changes land.

Changes include:

• Splitting out RemoteClipboard wrapper so that we can test other controls clipboard fully by remotely controlling the clipboard.
• Moving some useful test methods (runOperationInThread and waitAllEvents) to SwtTestUtil
• Improving SwtTestUtil.openShell on GTK4 so that all events needed to ensure shell is fully opened are received. In particular we used to just wait for SWT.Paint, however some operations, such as clipboard, cannot happen until SWT.Activate are also received.
• Added SwtTestUtil.waitAllEvents to support SwtTestUtil.openShell change
• Cleaned up Test_org_eclipse_swt_dnd_Clipboard now that I have better understanding how Clipboard works
• Added tests for selection clipboard by parameterizing most tests and adding new tests that check interaction between selection and normal clipboard
• Remove unneeded processEvents calls from Test_org_eclipse_swt_dnd_Clipboard

Part of #2126

[github-actions]

Test Results

  115 files  ±0    115 suites  ±0   9m 45s ⏱️ - 2m 43s
4 560 tests +6  4 544 ✅ +6  16 💤 ±0  0 ❌ ±0 
  311 runs  ±0    308 ✅ ±0   3 💤 ±0  0 ❌ ±0 

Results for commit 7ade0bb. ± Comparison against base commit d2de8e3.

This pull request removes 4 and adds 10 tests. Note that renamed tests count towards both.

org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_LocalClipboard
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_Remote
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_getContents
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_setContents

org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_LocalClipboard(int)[1]
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_LocalClipboard(int)[2]
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_Remote(int)[1]
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_Remote(int)[2]
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_getContents(int)[1]
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_getContents(int)[2]
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_getContentsBothClipboards
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_setContents(int)[1]
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_setContents(int)[2]
org.eclipse.swt.tests.junit.Test_org_eclipse_swt_dnd_Clipboard ‑ test_setContentsBothClipboards