Code fix to extract a type / variable / func to a shared file with imports

If a user writes:
```bicep
type ContainerImage = {
registry: string
name: string
tag: string
}

param image ContainerImage
```

It would be nice to offer a code fix to generate the following:
```bicep
import { ContainerImage } from ''

param image ContainerImage
```

Where the user gets to pick `` (either pick existing or create new), and the contents include:

```bicep
@export()
type ContainerImage = {
registry: string
name: string
tag: string
}
```

No files or tests are named. Start by locating the existing code-fix and import-handling entry points, then trace how a destination file is selected or created. Done means the example type can be extracted with @export(), an import is generated, and the original declaration is removed.

Written by the indexing model from the issue text.