Make css-minimizer compatible with webpack 5

[timneutkens]

Fixes some deprecation warnings during next build

[ijjk]

Stats from current PR

Default Server Mode (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
buildDuration	12.6s	11.9s	-711ms
nodeModulesSize	57.6 MB	57.6 MB	⚠️ +2.3 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.424	2.252	-0.17
/ avg req/sec	1031.16	1110.07	+78.91
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.401	1.541	⚠️ +0.14
/error-in-render avg req/sec	1784.78	1622.81	⚠️ -161.97

Client Bundles (main, webpack, commons)

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
677f882d2ed8..2585.js gzip	10.2 kB	10.2 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-6984394..c1c4.js gzip	6.72 kB	6.72 kB	✓
webpack-e067..f178.js gzip	751 B	751 B	✓
Overall change	56.7 kB	56.7 kB	✓

Client Bundles (main, webpack, commons) Modern

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
677f882d2ed8..dule.js gzip	6.07 kB	6.07 kB	✓
framework.HA..dule.js gzip	39 kB	39 kB	✓
main-85be351..dule.js gzip	5.79 kB	5.79 kB	✓
webpack-07c5..dule.js gzip	751 B	751 B	✓
Overall change	51.6 kB	51.6 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
polyfills-4b..e242.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
_app-9a0b9e1..b37e.js gzip	1.28 kB	1.28 kB	✓
_error-1464c..a26f.js gzip	3.44 kB	3.44 kB	✓
hooks-89731c..c609.js gzip	887 B	887 B	✓
index-17468f..5d83.js gzip	227 B	227 B	✓
link-00b8972..6e4e.js gzip	1.3 kB	1.3 kB	✓
routerDirect..924c.js gzip	284 B	284 B	✓
withRouter-7..c13d.js gzip	284 B	284 B	✓
Overall change	7.7 kB	7.7 kB	✓

Client Pages Modern

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
_app-75d3a82..dule.js gzip	625 B	625 B	✓
_error-e550f..dule.js gzip	2.29 kB	2.29 kB	✓
hooks-cbf13f..dule.js gzip	387 B	387 B	✓
index-b9a643..dule.js gzip	226 B	226 B	✓
link-72c64d9..dule.js gzip	1.27 kB	1.27 kB	✓
routerDirect..dule.js gzip	284 B	284 B	✓
withRouter-f..dule.js gzip	282 B	282 B	✓
Overall change	5.36 kB	5.36 kB	✓

Client Build Manifests

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
_buildManifest.js gzip	322 B	322 B	✓
_buildManife..dule.js gzip	330 B	330 B	✓
Overall change	652 B	652 B	✓

Rendered Page Sizes

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
index.html gzip	949 B	949 B	✓
link.html gzip	955 B	955 B	✓
withRouter.html gzip	942 B	942 B	✓
Overall change	2.85 kB	2.85 kB	✓

---

Serverless Mode

General Overall increase ⚠️

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
buildDuration	13.6s	13.5s	-99ms
nodeModulesSize	57.6 MB	57.6 MB	⚠️ +2.3 kB

Client Bundles (main, webpack, commons)

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
677f882d2ed8..2585.js gzip	10.2 kB	10.2 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-6984394..c1c4.js gzip	6.72 kB	6.72 kB	✓
webpack-e067..f178.js gzip	751 B	751 B	✓
Overall change	56.7 kB	56.7 kB	✓

Client Bundles (main, webpack, commons) Modern

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
677f882d2ed8..dule.js gzip	6.07 kB	6.07 kB	✓
framework.HA..dule.js gzip	39 kB	39 kB	✓
main-85be351..dule.js gzip	5.79 kB	5.79 kB	✓
webpack-07c5..dule.js gzip	751 B	751 B	✓
Overall change	51.6 kB	51.6 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
polyfills-4b..e242.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
_app-9a0b9e1..b37e.js gzip	1.28 kB	1.28 kB	✓
_error-1464c..a26f.js gzip	3.44 kB	3.44 kB	✓
hooks-89731c..c609.js gzip	887 B	887 B	✓
index-17468f..5d83.js gzip	227 B	227 B	✓
link-00b8972..6e4e.js gzip	1.3 kB	1.3 kB	✓
routerDirect..924c.js gzip	284 B	284 B	✓
withRouter-7..c13d.js gzip	284 B	284 B	✓
Overall change	7.7 kB	7.7 kB	✓

Client Pages Modern

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
_app-75d3a82..dule.js gzip	625 B	625 B	✓
_error-e550f..dule.js gzip	2.29 kB	2.29 kB	✓
hooks-cbf13f..dule.js gzip	387 B	387 B	✓
index-b9a643..dule.js gzip	226 B	226 B	✓
link-72c64d9..dule.js gzip	1.27 kB	1.27 kB	✓
routerDirect..dule.js gzip	284 B	284 B	✓
withRouter-f..dule.js gzip	282 B	282 B	✓
Overall change	5.36 kB	5.36 kB	✓

Client Build Manifests

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
_buildManifest.js gzip	322 B	322 B	✓
_buildManife..dule.js gzip	330 B	330 B	✓
Overall change	652 B	652 B	✓

Serverless bundles

	vercel/next.js canary	timneutkens/next.js fix/css-minimizer-webpack5-deprecation-message	Change
_error.js	1.03 MB	1.03 MB	✓
404.html	4.18 kB	4.18 kB	✓
hooks.html	3.82 kB	3.82 kB	✓
index.js	1.03 MB	1.03 MB	✓
link.js	1.07 MB	1.07 MB	✓
routerDirect.js	1.06 MB	1.06 MB	✓
withRouter.js	1.06 MB	1.06 MB	✓
Overall change	5.27 MB	5.27 MB	✓

Commit: 08de2f2