Fix no-server-import-in-page eslint rule for subfolder middleware

[thibautsabot]

People have been reporting on #30973 that the no-server-import-in-page eslint rule is reporting false positives for _middleware files inside sub-page folders.

Unlike _document, we can have multiple _middleware files.

Fixes #32121

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall decrease ✓

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
buildDuration	19.7s	19.6s	-92ms
buildDurationCached	3.6s	3.5s	-56ms
nodeModulesSize	347 MB	347 MB	-1 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.342	3.187	-0.16
/ avg req/sec	748.08	784.51	+36.43
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.453	1.562	⚠️ +0.11
/error-in-render avg req/sec	1720.44	1600.7	⚠️ -119.74

Client Bundles (main, webpack, commons)

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	28.4 kB	28.4 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.3 kB	72.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	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	326 B	326 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	4.49 kB	4.49 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	thibautsabot/next.js fix-no-server-import-in-page	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
index.html gzip	532 B	532 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Increase detected ⚠️)

General Overall decrease ✓

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
buildDuration	21.2s	21.4s	⚠️ +179ms
buildDurationCached	3.6s	3.6s	⚠️ +25ms
nodeModulesSize	347 MB	347 MB	-1 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.295	3.252	-0.04
/ avg req/sec	758.77	768.86	+10.09
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.491	1.492	0
/error-in-render avg req/sec	1677.27	1675.52	⚠️ -1.75

Client Bundles (main, webpack, commons)

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	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	thibautsabot/next.js fix-no-server-import-in-page	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	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	2.37 kB	2.37 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	622 B	622 B	✓
image-HASH.js gzip	4.53 kB	4.53 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	1.9 kB	1.9 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	13.3 kB	13.3 kB	✓

Client Build Manifests

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
_buildManifest.js gzip	458 B	458 B	✓
Overall change	458 B	458 B	✓

Rendered Page Sizes

	vercel/next.js canary	thibautsabot/next.js fix-no-server-import-in-page	Change
index.html gzip	532 B	532 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	525 B	525 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: 89a7097