fix(turbopack): don't match empty route groups

[ForsakenHarmony]

What?

Previously the matching just used the last match for children which could lead to empty groups or groups without page matches overriding the actual page.

This PR makes sure this doesn't happen and emits an issue (which unfortunately doesn't get displayed yet) in case there are 2 page matches which would go into the children slot.

Closes WEB-1895

[ijjk]

Stats from current PR

Default Build

General

	vercel/next.js canary	vercel/next.js hrmny/fix-group-matching	Change
buildDuration	12.4s	12.5s	N/A
buildDurationCached	6.9s	7s	N/A
nodeModulesSize	175 MB	175 MB	✓
nextStartRea..uration (ms)	436ms	458ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js hrmny/fix-group-matching	Change
199-HASH.js gzip	30 kB	30 kB	N/A
3f784ff6-HASH.js gzip	53.2 kB	53.2 kB	✓
99.HASH.js gzip	182 B	182 B	✓
framework-HASH.js gzip	45.5 kB	45.5 kB	✓
main-app-HASH.js gzip	253 B	252 B	N/A
main-HASH.js gzip	33.1 kB	33.1 kB	N/A
webpack-HASH.js gzip	1.75 kB	1.75 kB	N/A
Overall change	98.9 kB	98.9 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js hrmny/fix-group-matching	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js hrmny/fix-group-matching	Change
_app-HASH.js gzip	206 B	205 B	N/A
_error-HASH.js gzip	182 B	180 B	N/A
amp-HASH.js gzip	506 B	505 B	N/A
css-HASH.js gzip	322 B	323 B	N/A
dynamic-HASH.js gzip	2.59 kB	2.59 kB	✓
edge-ssr-HASH.js gzip	260 B	259 B	N/A
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	369 B	369 B	✓
image-HASH.js gzip	4.38 kB	4.38 kB	N/A
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.67 kB	2.67 kB	N/A
routerDirect..HASH.js gzip	316 B	318 B	N/A
script-HASH.js gzip	385 B	384 B	N/A
withRouter-HASH.js gzip	319 B	319 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	3.99 kB	3.99 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js hrmny/fix-group-matching	Change
_buildManifest.js gzip	484 B	482 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js hrmny/fix-group-matching	Change
index.html gzip	529 B	529 B	✓
link.html gzip	542 B	543 B	N/A
withRouter.html gzip	524 B	525 B	N/A
Overall change	529 B	529 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js hrmny/fix-group-matching	Change
edge-ssr.js gzip	96.1 kB	96.1 kB	N/A
page.js gzip	140 kB	140 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js hrmny/fix-group-matching	Change
middleware-b..fest.js gzip	625 B	624 B	N/A
middleware-r..fest.js gzip	150 B	151 B	N/A
middleware.js gzip	23 kB	23 kB	N/A
edge-runtime..pack.js gzip	1.92 kB	1.92 kB	✓
Overall change	1.92 kB	1.92 kB	✓

Commit: d2721d6

[ijjk]

Tests Passed