Allow reading request bodies in middlewares (#34294)

[javivelasco]

This PR brings back @Schniz awesome contribution to bring in bodies to middleware. It was reverted to leave it out of the stable release and to have some time to test it out in canary before officially releasing it. This PR is simply a cherry-pick of his original work.

Closes: #30953
Closes: #34490

[ijjk]

Had this re-opened here #34490 😅 we can re-land here though

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
buildDuration	16.1s	16.2s	⚠️ +106ms
buildDurationCached	6.4s	6.3s	-32ms
nodeModulesSize	359 MB	359 MB	⚠️ +6.07 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.189	3.091	-0.1
/ avg req/sec	783.85	808.88	+25.03
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.438	1.434	0
/error-in-render avg req/sec	1739.04	1743.06	+4.02

Client Bundles (main, webpack, commons)

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	27.9 kB	27.9 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.6 kB	71.6 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
_app-HASH.js gzip	1.36 kB	1.36 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	326 B	326 B	✓
dynamic-HASH.js gzip	2.57 kB	2.57 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	919 B	919 B	✓
image-HASH.js gzip	5.05 kB	5.05 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.26 kB	2.26 kB	✓
routerDirect..HASH.js gzip	321 B	321 B	✓
script-HASH.js gzip	383 B	383 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.7 kB	14.7 kB	✓

Client Build Manifests

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
index.html gzip	532 B	532 B	✓
link.html gzip	544 B	544 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
buildDuration	19.7s	19.6s	-135ms
buildDurationCached	6.4s	6.4s	-6ms
nodeModulesSize	359 MB	359 MB	⚠️ +6.07 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.116	3.141	⚠️ +0.02
/ avg req/sec	802.37	795.88	⚠️ -6.49
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.416	1.436	⚠️ +0.02
/error-in-render avg req/sec	1765.74	1741.53	⚠️ -24.21

Client Bundles (main, webpack, commons)

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.1 kB	42.1 kB	✓
main-HASH.js gzip	27.9 kB	27.9 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.7 kB	71.7 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	305 B	305 B	✓
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.56 kB	2.56 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	911 B	911 B	✓
image-HASH.js gzip	5.08 kB	5.08 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.28 kB	2.28 kB	✓
routerDirect..HASH.js gzip	314 B	314 B	✓
script-HASH.js gzip	375 B	375 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.7 kB	14.7 kB	✓

Client Build Manifests

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	javivelasco/next.js read-json-body	Change
index.html gzip	533 B	533 B	✓
link.html gzip	547 B	547 B	✓
withRouter.html gzip	527 B	527 B	✓
Overall change	1.61 kB	1.61 kB	✓

Commit: 795dbbb