This PR makes sure the `migrateImport` codemod is properly registered so
that it runs as part of the upgrade process.
## Test plan
This PR adds a new `v3` playground with an `upgrade` script that you can
use to run the upgrade from the local package. When you add a
non-prefixed `@import` to the v3 example, the paths are now properly
updated with no errors logged:
https://github.com/user-attachments/assets/85949bbb-756b-4ee2-8ac0-234fe1b2ca39
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Co-authored-by: Adam Wathan <4323180+adamwathan@users.noreply.github.com>
Co-authored-by: Philipp Spiess <hello@philippspiess.com>
