Serve public/ folder when page routes are disabled

[alreadyExisted]

Fixes: #9962
Closes: #9982
This PR fixed behavior on dev server when we has status 404 on files from public/ folder and

// next.config.js
module.exports = {
  useFileSystemPublicRoutes: false
}

[ijjk]

Stats from current PR

Default Server Mode

General Overall increase ⚠️

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
buildDuration	13s	13.3s	⚠️ +297ms
nodeModulesSize	48.9 MB	48.9 MB	⚠️ +974 B

Client Bundles (main, webpack, commons)

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
main-HASH.js gzip	5.11 kB	5.11 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
4952ddcd88e7..54d3.js gzip	4.68 kB	4.68 kB	✓
commons.HASH.js gzip	4.06 kB	4.06 kB	✓
de003c3a9d30..fffc.js gzip	13.7 kB	13.7 kB	✓
framework.HASH.js gzip	39.1 kB	39.1 kB	✓
Overall change	67.5 kB	67.5 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
main-HASH.module.js gzip	4.17 kB	4.17 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
4952ddcd88e7..dule.js gzip	5.56 kB	5.56 kB	✓
de003c3a9d30..dule.js gzip	12.5 kB	12.5 kB	✓
framework.HA..dule.js gzip	39.1 kB	39.1 kB	✓
Overall change	62.1 kB	62.1 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
polyfills-HASH.js gzip	4.76 kB	4.76 kB	✓
Overall change	4.76 kB	4.76 kB	✓

Client Pages

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
_app.js gzip	1.34 kB	1.34 kB	✓
_error.js gzip	4.07 kB	4.07 kB	✓
hooks.js gzip	779 B	779 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	2.9 kB	2.9 kB	✓
routerDirect.js gzip	283 B	283 B	✓
withRouter.js gzip	282 B	282 B	✓
Overall change	9.87 kB	9.87 kB	✓

Client Pages Modern

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
_app.module.js gzip	769 B	769 B	✓
_error.module.js gzip	3.06 kB	3.06 kB	✓
hooks.module.js gzip	371 B	371 B	✓
index.module.js gzip	212 B	212 B	✓
link.module.js gzip	2.47 kB	2.47 kB	✓
routerDirect..dule.js gzip	273 B	273 B	✓
withRouter.m..dule.js gzip	272 B	272 B	✓
Overall change	7.42 kB	7.42 kB	✓

Client Build Manifests

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Rendered Page Sizes

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
index.html gzip	1.02 kB	1.02 kB	✓
link.html gzip	1.03 kB	1.03 kB	✓
withRouter.html gzip	1.02 kB	1.02 kB	✓
Overall change	3.07 kB	3.07 kB	✓

---

Serverless Mode

General Overall increase ⚠️

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
buildDuration	13.9s	13.7s	-254ms
nodeModulesSize	48.9 MB	48.9 MB	⚠️ +974 B

Client Bundles (main, webpack, commons)

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
main-HASH.js gzip	5.11 kB	5.11 kB	✓
webpack-HASH.js gzip	746 B	746 B	✓
4952ddcd88e7..54d3.js gzip	4.68 kB	4.68 kB	✓
commons.HASH.js gzip	4.06 kB	4.06 kB	✓
de003c3a9d30..fffc.js gzip	13.7 kB	13.7 kB	✓
framework.HASH.js gzip	39.1 kB	39.1 kB	✓
Overall change	67.5 kB	67.5 kB	✓

Client Bundles (main, webpack, commons) Modern

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
main-HASH.module.js gzip	4.17 kB	4.17 kB	✓
webpack-HASH..dule.js gzip	746 B	746 B	✓
4952ddcd88e7..dule.js gzip	5.56 kB	5.56 kB	✓
de003c3a9d30..dule.js gzip	12.5 kB	12.5 kB	✓
framework.HA..dule.js gzip	39.1 kB	39.1 kB	✓
Overall change	62.1 kB	62.1 kB	✓

Legacy Client Bundles (polyfills)

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
polyfills-HASH.js gzip	4.76 kB	4.76 kB	✓
Overall change	4.76 kB	4.76 kB	✓

Client Pages

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
_app.js gzip	1.34 kB	1.34 kB	✓
_error.js gzip	4.07 kB	4.07 kB	✓
hooks.js gzip	779 B	779 B	✓
index.js gzip	222 B	222 B	✓
link.js gzip	2.9 kB	2.9 kB	✓
routerDirect.js gzip	283 B	283 B	✓
withRouter.js gzip	282 B	282 B	✓
Overall change	9.87 kB	9.87 kB	✓

Client Pages Modern

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
_app.module.js gzip	769 B	769 B	✓
_error.module.js gzip	3.06 kB	3.06 kB	✓
hooks.module.js gzip	371 B	371 B	✓
index.module.js gzip	212 B	212 B	✓
link.module.js gzip	2.47 kB	2.47 kB	✓
routerDirect..dule.js gzip	273 B	273 B	✓
withRouter.m..dule.js gzip	272 B	272 B	✓
Overall change	7.42 kB	7.42 kB	✓

Client Build Manifests

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
_buildManifest.js gzip	61 B	61 B	✓
_buildManife..dule.js gzip	61 B	61 B	✓
Overall change	122 B	122 B	✓

Serverless bundles

	zeit/next.js canary	alreadyExisted/next.js fix/public-directory-routes-on-dev-server	Change
_error.js gzip	70.9 kB	70.9 kB	✓
hooks.html gzip	1.05 kB	1.05 kB	✓
index.js gzip	71.3 kB	71.3 kB	✓
link.js gzip	80.6 kB	80.6 kB	✓
routerDirect.js gzip	78.2 kB	78.2 kB	✓
withRouter.js gzip	78.3 kB	78.3 kB	✓
Overall change	380 kB	380 kB	✓

Commit: 96fe3e3

[Timer]

Thanks for the fix!