refactor(vue): reuse script ast for rewriting default

[sxzz]

vuejs/core#7068 (review)

Description

Reuse the AST and MagicString instance from resolveScript.

Please don't merge it until the upstream PR got merged and released.

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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

• 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.

[sxzz]

Moving to https://github.com/vitejs/vite-plugin-vue