[build-utils][fs-detectors][cli] MAJOR: move some of build-utils into new fs-detectors (#8054)

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

packages/cli/src/util/dev/server.ts

@@ -36,12 +36,14 @@ import {
   StartDevServerResult,
   FileFsRef,
   PackageJson,
+  spawnCommand,
+} from '@vercel/build-utils';
+import {
   detectBuilders,
   detectApiDirectory,
   detectApiExtensions,
-  spawnCommand,
   isOfficialRuntime,
-} from '@vercel/build-utils';
+} from '@vercel/fs-detectors';
 import frameworkList from '@vercel/frameworks';
 
 import cmd from '../output/cmd';