[MNG-7269] Add multiple inheritance of parent projects

**[zosrothko](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=zosrothko)** opened **[MNG-7269](https://issues.apache.org/jira/browse/MNG-7269?redirect=false)** and commented

Hello Maven people

It would be nice to add the feature of multiples ihneritance of parent projects for any kind of module packaging. This would simplifies greatly the delivery of a software product build with  multi modules artifacts and by consequence the intégration of such products in a customer maven based application.

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No further details from [MNG-7269](https://issues.apache.org/jira/browse/MNG-7269?redirect=false)

Start by reading the linked MNG-7269 Jira report and the seven GitHub comments, since the issue provides no files, tests, or implementation entry point. Clarify the proposed multiple-parent behavior for all module packaging types and define completion around Maven supporting that behavior consistently.

Written by the indexing model from the issue text.