Make TargetReference conform to Hashable

[danieleformichelli]

Resolves https://github.com/tuist/tuist/issues/YYY
Request for comments document (if applies):

Short description 📝

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Checklist ✅

• The code architecture and patterns are consistent with the rest of the codebase.
• The changes have been tested following the documented guidelines.
• The PR includes the label changelog:added, changelog:fixed, or changelog:changed, whenever it should be included in the “Added”, “Fixed” or “Changed” section of the CHANGELOG. Note: when included in the CHANGELOG, the title of the PR will be used as entry, please make sure it is clear and suitable.
• In case the PR introduces changes that affect users, the documentation has been updated.
• In case the PR introduces changes that affect how the cache artifact is generated starting from the TuistGraph.Target, the Constants.cacheVersion has been updated.