middleware: add request referrer support

[Kikobeats]

closes: #30353

According with spec, 'about:client' is the default value is the user doesn't provide it.

It needs to add a test there, looks like there no unit tests for these classes 🤔

[timneutkens]

This is missing a test

[javivelasco]

Please add a test 🙏

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js referrer	Change
buildDuration	23.6s	23.4s	-206ms
buildDurationCached	4.4s	4.5s	⚠️ +100ms
nodeModulesSize	335 MB	335 MB	⚠️ +92 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	vercel/next.js referrer	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.897	3.943	⚠️ +0.05
/ avg req/sec	641.49	634.08	⚠️ -7.41
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	2.065	2.064	0
/error-in-render avg req/sec	1210.44	1210.99	+0.55

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js referrer	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	28.3 kB	28.3 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.2 kB	72.2 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js referrer	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js referrer	Change
_app-HASH.js gzip	1.37 kB	1.37 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	635 B	635 B	✓
image-HASH.js gzip	4.44 kB	4.44 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	1.87 kB	1.87 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	13.3 kB	13.3 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js referrer	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js referrer	Change
index.html gzip	523 B	523 B	✓
link.html gzip	536 B	536 B	✓
withRouter.html gzip	516 B	516 B	✓
Overall change	1.57 kB	1.57 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js referrer	Change
buildDuration	25.1s	25.4s	⚠️ +215ms
buildDurationCached	4.5s	4.5s	-12ms
nodeModulesSize	335 MB	335 MB	⚠️ +92 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	vercel/next.js referrer	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.947	4.098	⚠️ +0.15
/ avg req/sec	633.43	610.11	⚠️ -23.32
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	2.144	2.435	⚠️ +0.29
/error-in-render avg req/sec	1166.16	1026.54	⚠️ -139.62

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js referrer	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.6 kB	28.6 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	72.5 kB	72.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js referrer	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js referrer	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	2.38 kB	2.38 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	622 B	622 B	✓
image-HASH.js gzip	4.46 kB	4.46 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	1.91 kB	1.91 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	13.2 kB	13.2 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js referrer	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js referrer	Change
index.html gzip	524 B	524 B	✓
link.html gzip	535 B	535 B	✓
withRouter.html gzip	517 B	517 B	✓
Overall change	1.58 kB	1.58 kB	✓

Commit: db30749