fix: use experimental.viewTransition value for app.viewTransition if none set

[troyciesco]

🔗 Linked issue

#25547

❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

As part of 3.10 the intention was that if no value was set for app.viewTransition then it should automatically use the value of experimental.viewTransition.

It seems like that wasn't working because the experimental.viewTransition value wasn't available yet in the way it was referenced, so this PR fixes that.

No changes to docs are needed since this was the intended/documented behavior.

• Resolves app.viewTransition does not use the value from experimental.viewTransition #25547.
• Reference in release notes
• Original PR for the feature

📝 Checklist

• I have linked an issue or discussion.
• I have added tests (if possible).
• I have updated the documentation accordingly.

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.