and migrate o.e.e4.core.tests to use jakarta annotations.

All test-cases, besides the About-tests, are copied from
org.eclipse.e4.core.tests, before the migration of the latter.
Consequently o.e.e4.core.javax.tests only differ in the fact that the
former uses javax annotations, while the latter uses
jakarta annotations.

When support for javax annotations is removed from the E4-Injector,
o.e.e4.core.javax.tests can be deleted too.