Enable `ppr` when `dynamicIO` is enabled (#79302)
With this PR, we're automatically enabling `ppr` when `dynamicIO` is enabled, and forbid using `ppr: 'incremental'` or `ppr: false` together with `dynamicIO: true`.
While implementing the config validation, I noticed that the `userConfig`, `config`, and `result` objects in `assignDefaults` were untyped. This is fixed now.
