[MNG-6797] Remember in MavenSession that there were problems detected when building Maven model

**[Václav Haisman](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=wilx)** opened **[MNG-6797](https://issues.apache.org/jira/browse/MNG-6797?redirect=false)** and commented

Currently, Maven only prints few lines regarding Maven model problems it encounters when it is building the model. No plugin or code can retrieve the information anywhere. I would like to change that so that at least a boolean flag is used to remember that there were or were not problems when building Maven model.

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**Affects:** 3.6.2

**Attachments:**
- [pom.xml](https://issues.apache.org/jira/secure/attachment/12987213/pom.xml) (_1.39 kB_)
- [RequireNoMavenModelProblems.java](https://issues.apache.org/jira/secure/attachment/12987214/RequireNoMavenModelProblems.java) (_3.11 kB_)

**Remote Links:**
- [GitHub Pull Request #298
](https://github.com/apache/maven/pull/298)