api-regions-crossfeature-dups should work if all exports come from API Regions

The api-regions-crossfeature-dups analyser currently only works if exports are contributed from a feature that does not opt into the API Regions.

However it should also work for features that do opt into the API Regions. For such cases a 'defining' feature set should be specified. If any bundle exports a package into an API Region that is also exported by a bundle that's part of the defining region, this should trigger a error (or warning).