fix: code frame was not generated for postcss errors

[sapphi-red]

Description

Includes changes in #14984, please merge that one before

Code frame was not generated for PostCSS errors. This PR fixes that and reverts #6293 as it's now handled inside the plugin.
Also this PR fixes a bug that the caret position was not correct for PostCSS errors/warnings. PostCSS uses 1-based column unlike our generateCodeFrame.

I tested this PR with #5647 and #4667.

Additional context

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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, especially the Pull Request Guidelines.
• 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).
• Update the corresponding documentation if needed.
• Ideally, include relevant tests that fail without this PR but pass with it.