fix: normalize postcss dependency messages

[sibbng]

Description

It seems Vite normalizes dir-dependency messages but not dependency messages.

On my Windows machine, files defined in tailwind.config.js without glob patterns was not triggering HMR updates for CSS files.

Tailwind sends dependency message for non-glob patterns and dir-dependency message for glob patterns:
https://github.com/tailwindlabs/tailwindcss/blob/23b1b301a11178697db6f0b12785f99945fe0ef4/src/util/parseDependency.js#L35-L40

Take this config as reference:

  content: [
    './index.html',
    './src/App.vue',
    './src/components/**/*.vue',
  ],

Changes in files matching with ./src/components/**/*.vue pattern will trigger CSS HMR for those files, but changes in ./src/App.vue will not.

Reproduction:
https://github.com/sibbng/vite-tailwind-repro

Steps:

• Get a Windows machine
• Change bg color in App.vue, change will not trigger HMR for style.css
• Change bg color in HelloWorld.vue, change will trigger HMR for style.css and both div's background should be updated

Additional context

This issue could potentially fix #5808. But this bug report comes from a macOS user and there is no reproduction.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[Niputi]

could you add a test to the tailwind playground?

[sibbng]

could you add a test to the tailwind playground?

Done 👍