feat: add build.cssTarget option

[haoqunjiang]

Description

fixes #4746
fixes #5070
fixes #4930

Additional context

This option was discussed in previous meetings.
But I mistakenly thought #4658 had fixed the issue, so I didn't implement it until now.

The original PR made it possible to work around the issue in legacy browsers and projects without dynamic imports.

But in cases like #4746, if users target chrome61, import() will be transformed by esbuild to require(), leading to errors.

So we have to add this new option.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• 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.

[patak-cat]

Should we call this build.cssTarget in case there are other transforms apart from minification affected in the future?

[haoqunjiang]

Yeah, makes sense.

[winterkind]

Hi, may I ask what the label "on hold" means? No complaints, I am just the one who opened #4930 and trying to plan my next steps regarding it.

[patak-cat]

Hi, may I ask what the label "on hold" means?

We want to discuss the naming of the option with the rest of the team before merging. This PR is probably going to be part of next week's release.

[IainZhuo]

Hi, may I ask what the label "on hold" means?

We want to discuss the naming of the option with the rest of the team before merging. This PR is probably going to be part of next week's release.

What is the final name after the discussion? I want to find a description of this configuration on the documentation.

[patak-cat]

It will be build.cssTarget