put app code into a separate layer

[sokra]

What?

app code is different from pages code and need to be in a separate layer

Why?

Otherwise it tries to share chunks and will cause conflicting writes

How?

Closes WEB-1778

[ijjk]

Stats from current PR

Default Build

General

	vercel/next.js canary	vercel/next.js sokra/chunking-app-fix	Change
buildDuration	10.4s	10.3s	N/A
buildDurationCached	6s	6s	N/A
nodeModulesSize	172 MB	172 MB	✓
nextStartRea..uration (ms)	533ms	530ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js sokra/chunking-app-fix	Change
199-HASH.js gzip	27.5 kB	27.5 kB	N/A
3f784ff6-HASH.js gzip	50.9 kB	50.9 kB	✓
99.HASH.js gzip	182 B	182 B	✓
framework-HASH.js gzip	45.3 kB	45.3 kB	✓
main-app-HASH.js gzip	254 B	250 B	N/A
main-HASH.js gzip	32.9 kB	32.9 kB	N/A
webpack-HASH.js gzip	1.75 kB	1.75 kB	N/A
Overall change	96.4 kB	96.4 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js sokra/chunking-app-fix	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js sokra/chunking-app-fix	Change
_app-HASH.js gzip	206 B	205 B	N/A
_error-HASH.js gzip	182 B	180 B	N/A
amp-HASH.js gzip	506 B	505 B	N/A
css-HASH.js gzip	322 B	323 B	N/A
dynamic-HASH.js gzip	2.57 kB	2.57 kB	N/A
edge-ssr-HASH.js gzip	260 B	259 B	N/A
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	369 B	369 B	✓
image-HASH.js gzip	4.35 kB	4.35 kB	N/A
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.64 kB	2.63 kB	N/A
routerDirect..HASH.js gzip	312 B	311 B	N/A
script-HASH.js gzip	385 B	384 B	N/A
withRouter-HASH.js gzip	307 B	308 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	1.08 kB	1.08 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js sokra/chunking-app-fix	Change
_buildManifest.js gzip	485 B	482 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js sokra/chunking-app-fix	Change
index.html gzip	530 B	530 B	✓
link.html gzip	542 B	542 B	✓
withRouter.html gzip	524 B	525 B	N/A
Overall change	1.07 kB	1.07 kB	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js sokra/chunking-app-fix	Change
edge-ssr.js gzip	93.8 kB	93.8 kB	N/A
page.js gzip	152 kB	152 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js sokra/chunking-app-fix	Change
middleware-b..fest.js gzip	625 B	624 B	N/A
middleware-r..fest.js gzip	150 B	151 B	N/A
middleware.js gzip	22.9 kB	22.9 kB	N/A
edge-runtime..pack.js gzip	1.92 kB	1.92 kB	✓
Overall change	1.92 kB	1.92 kB	✓

Commit: 8daf3af