[record_use] Static extensions

[dcharkes]

https://github.com/dart-lang/language/blob/main/working/0723-static-extensions/feature-specification.md

How would these work with

• Static call recording: Probably easy enough but we need to distinguish them from extension methods and static methods in classes.
• Const instances, can the constructors of static extensions be const?

[eernstg]

The support for constructors in extensions is currently being designed, so nothing has been settled 100%. However, it's a pretty safe bet that there will be support for constant redirecting factories.