feat(angular): add tailwind support for buildable libraries

[leosvelperez]

Current Behavior

When building a buildable library, Tailwind directives (e.g. @apply) are not processed because ng-packagr doesn't support Tailwind out of the box and it doesn't allow either to provide our own PostCSS configuration.

For more details see #6924 (comment).

Expected Behavior

Building a buildable library that uses Tailwind should correctly process any directive found in the stylesheets.

Given ng-packagr doesn't support Tailwind natively (as the @angular-devkit/build-angular:browser does) and it doesn't allow us to specify custom PostCSS config, we need to provide a different implementation that does support Tailwind natively. This provides a similar experience to Angular applications where Tailwind just works.

Related Issue(s)

Fixes #6924
Fixes #7965

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Status	Command
	nx affected --target=e2e --base=1e577e4068b43110b1658af7b7922891d3ce74da --head=beee24fbb64e7cabb639c1082964f607f9dd6a9c --exclude=e2e-react-native,e2e-detox,e2e-gatsby --parallel --max-parallel=1
	nx run-many --target=build --all --parallel=8
	nx run-many --target=build --all --parallel=8
	nx run-many --target=build --all --parallel=8
	nx affected --target=build --base=1e577e4068b43110b1658af7b7922891d3ce74da --head=beee24fbb64e7cabb639c1082964f607f9dd6a9c --parallel --max-parallel=3
	nx affected --target=test --base=1e577e4068b43110b1658af7b7922891d3ce74da --head=beee24fbb64e7cabb639c1082964f607f9dd6a9c --parallel --max-parallel=3
	nx build typedoc-theme

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[Coly010]

LGTM! 🎉

[github-actions]

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