Add scene loader tests

[HexaField]

Summary

Adds tests for the various json component scene loader functions. In future, this can be refactored to be specific to each loader rather than all together.

Checklist

• Pre-push checks pass npm run check
  • Linter passing via npm run lint
  • Unit & Integration tests passing via npm run test:packages
  • Docker build process passing via npm run build-client
• If this PR is still a WIP, convert to a draft
• When this PR is ready, mark it as "Ready for review"
• Changes have been manually QA'd
• Changes reviewed by at least 2 approved reviewers

References

#4081

Reviewers

@HexaField @speigg @NateTheGreatt