[record_use] Dart API: Should `RecordUse` live in `package:record_use`

[dcharkes]

@mosuem added class RecordUse to package:meta, should we consider moving it to package:record_use?

Pros:

• Discoverability: The input and output live in the same package.
• (Single dependency for both build hook and code.)

Cons:

• There is no actual relationship in code between the annotation used for the class and the output format.
• If we get build dependencies or private dependencies, then the json format only needs to be a private or build dependency, but the annotation needs to be an ordinary dependency.

cc @goderbauer