[DependencyInjection] Allow frozen containers to be dumped to graphviz
merged branch igorw/graphviz-frozen-container-2.0 (PR #7017)

This PR was merged into the 2.0 branch.

Commits
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bd0ad92 [DependencyInjection] Allow frozen containers to be dumped to graphviz

Discussion
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[DependencyInjection] Allow frozen containers to be dumped to graphviz

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

This PR replaces #7010.