Part of #2482

As part of building a project-specific PackageVersions.props file, a list of used dependencies should be built first. The list should not contain any manually maintained (pinned) versions, so simple re-use of Versions.props is not enough for the current use-case.

Since Darc already parses the dependency versions from the PackageVersions.props file, its logical can be re-used for completing the specified task.