[static-build] Add support for Build Output v3 detection (#7669)

Adds detection logic for a framework / build script outputting Build Output v3
format to the filesystem. In this case, `static-build` will simply stop processing
after the Build Command since deserialization happens in the build-container side
of things (this is different compared to the v1 output which gets handled in this
Builder. The reason for that is because the v3 output matches what `vc build`
outputs vs. v1 which is a different format).

packages/static-build/test/build-fixtures/09-build-output-v3/build.js

@@ -0,0 +1,7 @@
+const fs = require('fs');
+fs.mkdirSync('.vercel/output/static', { recursive: true });
+fs.writeFileSync('.vercel/output/config.json', '{}');
+fs.writeFileSync(
+  '.vercel/output/static/index.html',
+  '<h1>Build Output API</h1>'
+);

packages/static-build/test/build-fixtures/09-build-output-v3/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "09-build-output-v3",
+  "private": true,
+  "scripts": {
+    "build": "node build.js"
+  }
+}