encode relationshipsByLanguage and orphanRelationships in dump-unified-graph

[QuietMisdreavus]

Bug/issue #, if applicable: None

Summary

When #28 landed, the code for dump-unified-graph was not updated to use the new relationship data. This PR updates the Encodable extension on UnifiedSymbolGraph to use the relationshipsByLanguage and orphanRelationships properties instead of the old unified relationships property. This removes a deprecation warning when building SymbolKit.

Dependencies

None

Testing

Rerun the testing instructions for #29. The Xcode 14 beta will generate multiple symbol graphs per-language, so passing the symbol-graph directory from a project's build folder to --symbol-graph-dir will work.

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• [ n/a ] Added tests
• Ran the ./bin/test script and it succeeded
• [ n/a ] Updated documentation if necessary

[QuietMisdreavus]

@swift-ci Please test

[kirillyakimovich]

Hey! Is there a plan to merge this?

[stefanpenner]

Bumping this — the deprecation warning on relationships in UnifiedSymbolGraph+Encodable.swift still fires on every build that uses rules_swift (e.g. via Bazel). Would be great to get this merged.