Turbopack: Fix slow filesystem benchmark warning for `next dev` (#89798)
Apparently we broke this about 6 months ago and didn't notice:
- We briefly had both a `println` (legacy) and a compilation event, leading to duplicate logging.
- First: https://github.com/vercel/next.js/pull/80631 - I added a filter to `backgroundLogCompilationEvents` that inadvertently filtered out `SlowFilesystemEvent` on dev.
- Around the same time: https://github.com/vercel/next.js/pull/81972 - This removed the old `println` in favor of the compilation event
Changes in this PR:
- Add `SlowFilesystemEvent` to the filter used in dev.
- Increase the threshold from 100ms to 200ms. I'm concerned that with Turbopack's File System cache, that the FS might be more heavily loaded during this benchmark than it was before, and I'd rather err on the "less aggressive" side.
- Add a link to https://nextjs.org/docs/app/guides/local-development, which now has documentation on the antivirus thing.
Tested with a threshold of 0ms:

There's not any easy way to test this, but it's also clearly not a big deal if it does break, as it's just a debugging hint for performance issues.