Add method for plugins to reference global dependencies

The new annotation versioning system allows plugins to share common
global interfaces that can be versioned on their own. To facilitate
this add a static method for plugins to get a hold of dependencies.
To get any dependency a plugin must @Requires it so it can be version
checked.

Test: Plugin that uses the new call.
Change-Id: I8e01260f8fbc14465502d506a7aa08212795ad9b