The code for these two are almost identical, so consolidate into one codebase.
Also adjusts the `pnpm test` script to allow for specifying a file name to be executed, instead of running all tests.
The `@vercel/build-utils` package was meant be shared functions necessary for writing a Vercel Builder (aka Runtime).
This package has since bloated into the catch-all package for anything that wasn't a Builder.
This PR removes the bloat in favor of a new package, `@vercel/fs-detectors`. It also removes the need for `@vercel/build-utils` to have a dependency on `@vercel/frameworks`.
- Related to #7951
