fix(navigation): allow useSelectedLayoutSegment(s) in Pages Router

[balazsorban44]

What?

Do not fail when useSelectedLayoutSegment or useSelectedLayoutSegments APIs are called in the Pages Router.

Why?

This makes migration easier and creates consistency with our other App Router-specific APIs that inherit the same behavior.

How?

Similar to #47490, we return null if there is no Layout context (indicating being in Pages Router)

Types are also overridden in the navigation compact module declaration which kicks in during start to correct the types if we detect a pages/ directory.

Note to reviewer: #47490 didn't add a test, so I added one top-level, let me know if you have a better suggestion for placing.

Closes NEXT-2506
Fixes #61464

[ijjk]

Tests Passed

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
buildDuration	13.9s	14.1s	⚠️ +166ms
buildDurationCached	8.8s	6.5s	N/A
nodeModulesSize	197 MB	197 MB	N/A
nextStartRea..uration (ms)	407ms	411ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
2453-HASH.js gzip	30.5 kB	30.5 kB	N/A
3304.HASH.js gzip	181 B	181 B	✓
3f784ff6-HASH.js gzip	53.7 kB	53.7 kB	N/A
8299-HASH.js gzip	5.04 kB	5.04 kB	N/A
framework-HASH.js gzip	45.2 kB	45.2 kB	✓
main-app-HASH.js gzip	241 B	242 B	N/A
main-HASH.js gzip	32.1 kB	32.2 kB	N/A
webpack-HASH.js gzip	1.7 kB	1.7 kB	N/A
Overall change	45.4 kB	45.4 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
_app-HASH.js gzip	196 B	197 B	N/A
_error-HASH.js gzip	184 B	184 B	✓
amp-HASH.js gzip	505 B	505 B	✓
css-HASH.js gzip	324 B	325 B	N/A
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edge-ssr-HASH.js gzip	258 B	258 B	✓
head-HASH.js gzip	352 B	352 B	✓
hooks-HASH.js gzip	370 B	371 B	N/A
image-HASH.js gzip	4.2 kB	4.2 kB	✓
index-HASH.js gzip	259 B	259 B	✓
link-HASH.js gzip	2.67 kB	2.67 kB	N/A
routerDirect..HASH.js gzip	314 B	312 B	N/A
script-HASH.js gzip	386 B	386 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	6.56 kB	6.56 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
_buildManifest.js gzip	483 B	485 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
index.html gzip	529 B	527 B	N/A
link.html gzip	542 B	540 B	N/A
withRouter.html gzip	524 B	522 B	N/A
Overall change	0 B	0 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
edge-ssr.js gzip	95.1 kB	95 kB	N/A
page.js gzip	3.06 kB	3.06 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
middleware-b..fest.js gzip	624 B	626 B	N/A
middleware-r..fest.js gzip	151 B	151 B	✓
middleware.js gzip	25.5 kB	25.5 kB	N/A
edge-runtime..pack.js gzip	839 B	839 B	✓
Overall change	990 B	990 B	✓

Next Runtimes

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
app-page-exp...dev.js gzip	171 kB	171 kB	N/A
app-page-exp..prod.js gzip	96.7 kB	96.7 kB	N/A
app-page-tur..prod.js gzip	98.5 kB	98.5 kB	N/A
app-page-tur..prod.js gzip	92.9 kB	92.9 kB	N/A
app-page.run...dev.js gzip	150 kB	150 kB	N/A
app-page.run..prod.js gzip	91.4 kB	91.4 kB	N/A
app-route-ex...dev.js gzip	21.3 kB	21.3 kB	✓
app-route-ex..prod.js gzip	15 kB	15 kB	✓
app-route-tu..prod.js gzip	15 kB	15 kB	✓
app-route-tu..prod.js gzip	14.8 kB	14.8 kB	✓
app-route.ru...dev.js gzip	20.9 kB	20.9 kB	✓
app-route.ru..prod.js gzip	14.8 kB	14.8 kB	✓
pages-api-tu..prod.js gzip	9.51 kB	9.51 kB	✓
pages-api.ru...dev.js gzip	9.79 kB	9.79 kB	✓
pages-api.ru..prod.js gzip	9.51 kB	9.51 kB	✓
pages-turbo...prod.js gzip	22.3 kB	22.3 kB	✓
pages.runtim...dev.js gzip	23 kB	23 kB	✓
pages.runtim..prod.js gzip	22.3 kB	22.3 kB	✓
server.runti..prod.js gzip	50.6 kB	50.6 kB	N/A
Overall change	198 kB	198 kB	✓

build cache Overall increase ⚠️

	vercel/next.js canary	vercel/next.js fix/use-selected-layout-segment-s-pages	Change
0.pack gzip	1.56 MB	1.56 MB	N/A
index.pack gzip	105 kB	105 kB	⚠️ +118 B
Overall change	105 kB	105 kB	⚠️ +118 B

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Commit: fd9456c