fix: Avoid importing in source that __vitePreload has declared (close #4016)

[xingxiuyi]

fix: Avoid importing in source that __vitePreload has declared (close #4016)

Description

this pull request fix #4016 (Error: Identifier '__vitePreload' has already been declared)

Additional context

If the Identifier '__vitePreload' has already been declared, there is no need to repeat the import

Use this simple project to verify: https://github.com/xingxiuyi/test-vite-async-import

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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