fix(postcss): preserve interpolations and indentation through stylelint --fix

[Anber]

Fixes #1494.

Summary

• Read the re-indented declaration value from raws.value.raw rather than value. PostCSS strips comments out of value, and an interpolation alone on its own line inside a parenthesised value is represented as a comment placeholder, so it was already gone before the stringifier ran.
• Teach substitutePlaceholders the comment placeholder form. Its scan splits on spaces and cannot see /* pcss-lin:N */, whose delimiters are separate tokens.
• Substitute at-rule params where the stringifier reads them. super.atrule re-reads params through rawValue, so substituting into node.params was discarded whenever the params spanned lines, and @media screen and ${query} came out as @media screen and .pcss-lin0.
• Substitute placeholders in the afterName raw as well. An interpolation on the line after the at-rule name lands there instead of in the params and was emitted verbatim.
• Restore base indentation for afterName, which computeBeforeAfter never handled. A wrapped at-rule prelude lost its leading whitespace on any fix, templates containing no interpolations at all included.

The last three problems are older than this issue and surfaced while testing the first. They all have the same cause: the stringifier reads from somewhere other than where the substitution was written. They also live in the same two files, so they are fixed here rather than left for a follow-up.

Validation

• pnpm --filter @linaria/postcss-linaria test: 84 tests, 6 of them new. All 6 fail without the source changes, and no existing test is affected.
• pnpm --filter @linaria/postcss-linaria typecheck
• pnpm --filter @linaria/postcss-linaria build
• pnpm check:all
• End to end through the Stylelint CLI with a real fixable rule enabled. Before, --fix makes three unwanted edits alongside the intended ones: a leaked /* pcss-lin:0 */, a .pcss-lin1 where a media query should be, and a dropped interpolation. After, only the intended edits. A separate file with a wrapped @media prelude and no interpolations loses four spaces of indentation before, and is untouched after.

[changeset-bot]

🦋 Changeset detected

Latest commit: c3a0f90

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 9 packages

Name	Type
@linaria/postcss-linaria	Patch
@linaria/atomic	Patch
@linaria/babel-plugin-interop	Patch
@linaria/core	Patch
@linaria/react	Patch
@linaria/server	Patch
@linaria/stylelint	Patch
@linaria/stylelint-config-standard-linaria	Patch
linaria	Patch

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