Use regular Maven coordinates -when possible- for dependencies

[mickaelistria]

Currently, running mvn dependency:list for a Tycho module lists all dependencies under the form p2-installable-unit:org.domain.pluginId:version (eg p2-installable-unit:org.mockito.mockito-core:4.1.0). The scope is usually system and the absolute path to file is set.
In case where the dependency is known to have Maven coordinates, it would be better to reuse the coordinates of this dependency to showcase it's the "official" artifact from Maven repo. So in case of Mockito, it would become org.mockito:mockito-core:4.1.0. p2 metadata are expected to contain the necessary info to map a p2 artifact/unit back to the Maven coordinates they're generated from, those data should then be used in P2ResolverImpl when calling result.addArtifact to not hardcode usage of ArtifactType.TYPE_INSTALLABLE_UNIT and let Maven coordinates be used in place.
I expect that as long as the scope remains system and path is hardcoded, this shouldn't be too disruptive.

[akurtakov]

It's closely related to eclipse-dash/dash-licenses#125 and this might fix the dash-licenses bug even.

[mickaelistria]

One hotspot would be MavenDependencyInject#injectMavenDependencies()

[laeubi]

Just one thing that came into my mind, given we have a repository of type p2 specified, it should be possible to even resolve p2-installable-unit:<unit>:<version> in a regular maven build using a core extension in .mvn folder. That would then download the unit from the repository and set the appropriate path before the actual build start.

[mickaelistria]

Some incremental work can be done to ease implementation of this feature:

• Remove P2ResolutionResults.Entry and use ArtifactDescriptor instead in P2ResolutionResult
• Add a getMavenCoordinates() method, returning a GAV to ArtifactDescriptor
• Make P2DependencyResolver set the Maven coordinates for given ArtifactDescriptor according to p2 metadata
• Make MavenDependencyInject#injectMavenDependencies() consume the GAV when available to populate dependencies instead of using the ArtifactKey (which is p2 more than Maven).