feat: support tailwind v4

[heddendorp]

PR Checklist

Please check to confirm your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

The current integration if for tailwind V3 only.

Issue Number: #28938

What is the new behavior?

Detect if tailwind v4 is used as indicated by the presence of the @tailwindcss/postcss package. If so, check that also tailwindcss is installed. If both are present, Add the tailwind postCSS plugin.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[pumano]

would be good to have same support for esbuild builder too, not only for webpack

[heddendorp]

would be good to have same support for esbuild builder too, not only for webpack

Agreed, I found what seems to be the correct place here https://github.com/angular/angular-cli/pull/28939/files#diff-c31d390b8683db112fcc30e2ee984d893bdce6bd8e6d7d70c43ecc410a626a3dR489
But I am unsure how to add it correctly for the application builder.

[clydin]

would be good to have same support for esbuild builder too, not only for webpack

The application build system supports custom postcss configuration via either a postcss.config.json or .postcssrc.json file. Note that this can lead to increased build times since postcss is otherwise unused in the application build system and is only enabled if tailwind and/or a postcss configuration file is present.

[sheikalthaf]

@clydin tailwind v4 is getting released next week, it is better have support from day 1

[DominicWrege]

Can't wait to get this feature

[clydin]

If you are interested in updating to or trying out Tailwind v4, ensure the project is using the application build system (default for new projects) and please follow the instructions found in the Tailwind documentation: https://tailwindcss.com/docs/installation/framework-guides/angular

[Kludgy4]

The largest change in Tailwind v4 is the extra speed from their new build system, which we can't fully appreciate with postcss mandated. I'd say it's essential this PR, or a following one, allows us to use tailwindcss without postcss