[FrameworkBundle] adds routing/container descriptors
feature #7887 [FrameworkBundle] adds routing/container descriptors (jfsimon)

This PR was squashed before being merged into the master branch (closes #7887).

Discussion
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[FrameworkBundle] adds routing/container descriptors

The goal of this PR is to add descriptors (as in #7454) for routing and container. This will permit add a `--format` option to `router:debug` and `container:debug` commands (with `txt`, `json`, `xml` and `md` formats).

Commits
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22f9bc8 [FrameworkBundle] adds routing/container descriptors