[Fixes #59364968]  Added a third party p2 repository generator/jetty host under eclipse-thirdparty-p2.

- Added scripts to rebuild and start/stop the p2 Software Site outside of the regular maven build.
- Added Eclipse plug-in for running eclipse plug-in tests (run in a UI harness).
- Added target definition that references juno, orbit, and local 3rd party p2 repository for maintaining a consistent target platform for eclipse development and build.
- Put in a placeholder class and corresponding test (AnalysisEngineImpl) to show that maven dependency assertj can be used alongside other plug-ins.
- Included a third party jar com.google.guava) in the feature to prove that the tycho build for update site will include third party dependencies generated from p2-maven-plugin when creating the update site.
 *** This is important, since these are plug-ins that are not known to be in a public p2 repository.