feat(css): add cssExtract option to build config (#4345)

[JackFGreen]

Description

Add cssExtract option.
When building as a library, you can also set this to false to avoid your users having to import the CSS themselves, like vue-cli css.extract

fix #4345

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What is the purpose of this pull request?

• [ ] Bug fix
• [x] New Feature
• [ ] Documentation update
• [ ] Other

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

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

[Djaler]

I published this in my fork: @djaler/[email protected]

[bluwy]

Looks there are failing tests before it can be reviewed.

[Djaler]

@JackFGreen can you update this?

[JackFGreen]

@JackFGreen can you update this?

@Djaler updated, check the new version

[seahindeniz]

@JackFGreen there's a failed test that might require your attention