fix: Represent string literals as single-value unions

[jperals]

Issue #, if available:

Description of changes:

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[codecov]

Codecov Report

❌ Patch coverage is 86.36364% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.42%. Comparing base (2753437) to head (6afcffb).

Files with missing lines	Patch %	Lines
src/components/object-definition.ts	86.36%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #106      +/-   ##
==========================================
- Coverage   96.68%   96.42%   -0.27%     
==========================================
  Files          11       11              
  Lines         845      867      +22     
  Branches      290      290              
==========================================
+ Hits          817      836      +19     
- Misses         28       31       +3     

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