It may be that this test fails regularly because
another test is not cleaned up properly.
Make sure there are no unexpected projects in
the workspace.

Part of eclipse-cdt#117

Part of eclipse-cdt#117

This old test had a race condition. The failing test was trying
to verify that CDTPROJECT_ADDED was received, but if there
was a delay in the startup then another event would come in
later. So for this test use the first received event,
for the remaining tests use the last received event.

Part of eclipse-cdt#117

On GitHub actions the org.eclipse.cdt.ui.tests.text.contentassist2
tests are running after ProposalFilterPreferencesTest and
ProposalFilterPreferencesTest was changing the default
filter and not restoring it.

Part of eclipse-cdt#117

Part of eclipse-cdt#117

Various tests are not cleaning up properly after
themselves, causing test failures on subsequent
tests. Therefore start each test by deleting
all projects.

In addition, some tests were creating their test
projects in their constructor. As all the constructors
run before all the tests as part of test discovery
it means that projects were being created in
constructor and interfering with other tests
later. With the deleting of all projects in @AfterEach
these tests would have started failing. Therefore,
change these tests to create their projects
and do other initialize tasks in the setUp method.

For older JUnit3 style tests:
This substantially slows down tests as many tests
rely on sharing the project between multiple tests and
recreating those projects on each run is slow.
Therefore this is not applied universally to
all JUnit3 tests.

For tests that are affected, those tests are moved
to JUnit5 base test.

Part of eclipse-cdt#117