GraphizDumper now displays unresolved parameters

Previously it would crash when given a container with an unresolved
parameter. This change will instead show the parameter name on the
final diagram, instead of the class name.
feature #10880 [DependencyInjection] GraphvizDumper now displays unresolved parameters (rosstuck)

This PR was merged into the 2.5-dev branch.

Discussion
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[DependencyInjection] GraphvizDumper now displays unresolved parameters

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | none

Previously, the graphviz dumper would throw an exception if given a container with an unresolved parameter. This change allows it to render the parameter name instead of the class name if the class can not be resolved. This is also closer to the other DI dumpers which do not error out in these circumstances but simply carry the parameter name over.

For a practical use case, see: https://github.com/rosstuck/TuckConverterBundle/issues/1

Commits
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f800e15 GraphizDumper now displays unresolved parameters