Support new `next.config.ts` config file.
Had to do some weird gymnastics around `swc` in order to use it within
unit tests. Had to pass through the `parsed.span.end` value of any
previous iteration and account for it.
Looks to be an open issue here:
https://github.com/swc-project/swc/issues/1366Fixes#7318
a64f37e014