add tracing for turbopack (vercel#49920)

### What?

adds `NEXT_TURBOPACK_TRACING` env var to enable tracing. Writes into `.next/trace.log`

There are 4 presets:

* `NEXT_TURBOPACK_TRACING=overview` gives a overview of requests and modules processed.
* `NEXT_TURBOPACK_TRACING=next` above plus details for next.js
* `NEXT_TURBOPACK_TRACING=turbopack` above plus details for turbopack
* `NEXT_TURBOPACK_TRACING=turbo-tasks` above plus details for turbo-tasks

Published release builds will only allow `overview` to work, since all detailed instrumentation is statically disabled.

see vercel/turborepo#4966 for more details

### Why?

get more insight into build times

### Turbopack changes

* vercel/turborepo#4995 
* vercel/turborepo#5049 
* vercel/turborepo#5053 
* vercel/turborepo#4966