561574: Virgo Tools do not work on Eclipse 2019-06 or later

Change pom.xml to pull Libra from Jenkins CI build using
jar URL.

Change super-type of ProjectBundleRoot from JarPackageFragmentRoot to
ExternalPackageFragmentRoot to avoid the need to use the new constructor
of JarPackageFragmentRoot only available in Eclipse 2019-12 or later
2 files changed