Ensure only backslashes are in pages-manifest with i18n

[ijjk]

This ensures the pages-manifest only includes forward slashes and not backslashes when adding i18n page references, this also adds tests ensuring we don't regress on this in the i18n-support test suite.

Fixes: #20330

[ijjk]

Stats from current PR

Default Server Mode (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
buildDuration	8.6s	8.7s	⚠️ +151ms
nodeModulesSize	82.6 MB	82.6 MB	⚠️ +125 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
/ failed reqs	0	0	✓
/ total time (seconds)	1.708	1.712	0
/ avg req/sec	1463.7	1460.24	⚠️ -3.46
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.084	1.078	-0.01
/error-in-render avg req/sec	2306.53	2318.54	+12.01

Client Bundles (main, webpack, commons)

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
677f882d2ed8..5e70.js gzip	12.8 kB	12.8 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-72193d1..1356.js gzip	6.56 kB	6.56 kB	✓
webpack-95c2..e870.js gzip	751 B	751 B	✓
Overall change	59 kB	59 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
polyfills-d3..23f6.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
_app-0d19cb6..5497.js gzip	1.28 kB	1.28 kB	✓
_error-85785..a9f3.js gzip	3.44 kB	3.44 kB	✓
hooks-42456f..0c06.js gzip	887 B	887 B	✓
index-8081ce..e44f.js gzip	227 B	227 B	✓
link-0ab9f83..fa00.js gzip	1.61 kB	1.61 kB	✓
routerDirect..c3d8.js gzip	303 B	303 B	✓
withRouter-0..a68e.js gzip	302 B	302 B	✓
Overall change	8.05 kB	8.05 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
_buildManifest.js gzip	323 B	323 B	✓
Overall change	323 B	323 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
index.html gzip	613 B	613 B	✓
link.html gzip	618 B	618 B	✓
withRouter.html gzip	607 B	607 B	✓
Overall change	1.84 kB	1.84 kB	✓

---

Serverless Mode

General Overall increase ⚠️

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
buildDuration	10.1s	10.2s	⚠️ +139ms
nodeModulesSize	82.6 MB	82.6 MB	⚠️ +125 B

Client Bundles (main, webpack, commons)

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
677f882d2ed8..5e70.js gzip	12.8 kB	12.8 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-72193d1..1356.js gzip	6.56 kB	6.56 kB	✓
webpack-95c2..e870.js gzip	751 B	751 B	✓
Overall change	59 kB	59 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
polyfills-d3..23f6.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
_app-0d19cb6..5497.js gzip	1.28 kB	1.28 kB	✓
_error-85785..a9f3.js gzip	3.44 kB	3.44 kB	✓
hooks-42456f..0c06.js gzip	887 B	887 B	✓
index-8081ce..e44f.js gzip	227 B	227 B	✓
link-0ab9f83..fa00.js gzip	1.61 kB	1.61 kB	✓
routerDirect..c3d8.js gzip	303 B	303 B	✓
withRouter-0..a68e.js gzip	302 B	302 B	✓
Overall change	8.05 kB	8.05 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
_buildManifest.js gzip	323 B	323 B	✓
Overall change	323 B	323 B	✓

Serverless bundles

	vercel/next.js canary	ijjk/next.js i18n/pages-manifest	Change
_error.js	1 MB	1 MB	✓
404.html	2.67 kB	2.67 kB	✓
hooks.html	1.92 kB	1.92 kB	✓
index.js	1 MB	1 MB	✓
link.js	1.06 MB	1.06 MB	✓
routerDirect.js	1.05 MB	1.05 MB	✓
withRouter.js	1.05 MB	1.05 MB	✓
Overall change	5.16 MB	5.16 MB	✓

Commit: adff871