Fix regression where SkyBox.show = false is ignored

[markschlosseratbentley]

Description

This PR fixes SkyBox.show being ignored when set to false. See linked issue for more details and discussion. This PR fixes a regression introduced by #13153 which refactored SkyBox to delegate to CubeMapPanorama.

Issue number and link

#13311

Testing plan

• Unit test added.
• Tested manually by locally trying it on PR Create partial reference implementation for BENTLEY_materials_planar_fill (behind) #13178

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @markschlosseratbentley!

✅ We can confirm we have a CLA on file for you.

[lukemckinstry]

I forgot to mention our strategy here was to have SkyBox implement and delegate all logic to CubeMapPanorama, I added a commit with that slight modification. Does this look ok to you @markschlosseratbentley ?

[markschlosseratbentley]

I forgot to mention our strategy here was to have SkyBox implement and delegate all logic to CubeMapPanorama, I added a commit with that slight modification. Does this look ok to you @markschlosseratbentley ?

@lukemckinstry LGTM 👍