fix: css content (v2)

[sapphi-red]

Description

I recommend not to squash when merging because each commit is quite different

This PR contains

• reverting fix(css): remove ?used hack (fixes #6421, #8245, #8461) #8471
  • this reopens
    • something is wrong with building when using '?inline' with css  #5348
    • CSS is missed in transform hook #6421
    • CSS Modules not included with import statment and resolve alias #8245
    • Vite version 2.9.2 and beyond don't honor external package CSS/Sass module inclusion in output bundle #8461
  • this fixes for v2
    • Vue build lib doubles css code #8819
    • CSS is included in SSR builds #8859
• add test (for v3: test: css content tests #8873)
  • CSS Modules not included with import statment and resolve alias #8245
  • Vite version 2.9.2 and beyond don't honor external package CSS/Sass module inclusion in output bundle #8461
• backport fix(css): preserve dynamic import css code (fix #5348) #7746
  • this fixes
    • something is wrong with building when using '?inline' with css  #5348
• skip test
  • CSS Modules not included with import statment and resolve alias #8245
  • Vite version 2.9.2 and beyond don't honor external package CSS/Sass module inclusion in output bundle #8461

so as a result this PR:

• fixes
  • Vue build lib doubles css code #8819
  • CSS is included in SSR builds #8859
• reopens
  • CSS is missed in transform hook #6421
  • CSS Modules not included with import statment and resolve alias #8245
  • Vite version 2.9.2 and beyond don't honor external package CSS/Sass module inclusion in output bundle #8461

Additional context

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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.

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