Add experimental compile/generate handling (#49491)
This implements experimental`compile`/`generate` commands to allow
separate the compilation and static generation steps of the build.
Initially this is for testing and follows same experimental rules which
aren't covered by semver.
Note: most changes are just spacing changes so disabling that in the
diff will be helpful.
x-ref: [initial
thread](https://www.notion.so/vercel/bbdbba2016ed464eb5263d325fecc02f?pvs=4)
x-ref: [slack
thread](https://vercel.slack.com/archives/C03DQ3QFV7C/p1676591260523589?thread_ts=1676554904.334789&cid=C03DQ3QFV7C)
