Validate configuration

[kneth]

What, How & Why?

This closes #3771

☑️ ToDos

• 📝 Changelog entry
• [ ] 📝 Compatibility label is updated or copied from previous entry
• 🚦 Tests
• [ ] 📝 Public documentation PR created or is not necessary
• [ ] 💥 Breaking label has been applied or is not necessary

If this PR adds or changes public API's:

• typescript definitions file is updated
• [ ] jsdoc files updated
• [ ] Chrome debug API is updated if API is available on React Native

[nirinchev]

Is disableFormatUpgrade an option compatible with sync? I would imagine that this would prevent Sync from writing to the file. Additionally, we should express these incompatibilities in the typescript definitions so that people who are using an editor that respects ts definitions will get early feedback if they try to construct an invalid config.

[takameyer]

Just a formatting issue that should be addressed.

I am not completely satisfied with how the typings resolve for configuration, but I have no alternative solution at the moment. If the developer explicitly uses ConfigurationWithSync, then the TS errors look nice, but if they use the Configuration union, the TS errors are quite vague. If I come up with a better solution later, I will make a separate PR.

Otherwise, LGTM