fix: Support `turbo.jsonc` in codemod transforms (#12532)
## Summary
- All codemod transforms hardcoded `path.join(root, "turbo.json")`,
causing migrations to fail with `No turbo.json found` on repos using
`turbo.jsonc`
- Exports `resolveTurboConfigPath` from `@turbo/utils` (was
module-private) and uses it across all 12 transforms to resolve either
`turbo.json` or `turbo.jsonc`
- Rewrites `getTurboRoot()` to check both filenames at each directory
level during the upward search, so a closer `turbo.jsonc` takes priority
over a parent `turbo.json`
- Updates `FileTransform` to parse `.jsonc` files with JSON5
## Testing
The string-based transforms (like `update-versioned-schema-json`)
preserve comments in `.jsonc` files since they operate on raw strings. A
new test + fixture verifies this end-to-end. Object-based transforms
(e.g. `rename-pipeline`) will strip comments since they parse to JSON
objects -- this is a pre-existing architectural limitation that would
require a comment-preserving serializer to fix.
