fix: output combined sourcemap in importAnalysisBuild plugin

[sapphi-red]

Description

Rollup v3 changed the way sourcemaps were handled (rollup/rollup#4605) but Vite's importAnalysisBuild plugin wasn't updated.
In rollup v2, editing chunk.map affected the output, but in v3 it's not the case.

fixes #12047
fixes #12634

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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