Add dataobjects

[cviebrock]

Description

• Converts 'SomeClass' to SomeClass::class throughout
• uses SwatDBClassMap::new() instead of instantiating class-name variables
• adds dataobject docblocks to the (one) data object class
• minor other changes to PHP logic and type hinting to help with static analysis

Testing Instructions (optional)

Add step-by-step instructions for testing the PR, if necessary.

1. Check out this PR
2. CI should pass

Developer Checklist

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complete:

• I added a link to the relevant Shortcut story, if applicable
• I added testing instructions, if any
• I made sure existing CI checks pass
• I checked that all requirements of the ticket are fulfilled

Reviewer Checklist

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• I made sure there are no active labels that block merge
• I followed the testing instructions
• I made sure the CI checks pass
• I reviewed the file changes on GitHub
• I checked that all requirements of the ticket (if any) are fulfilled