build: should generate Hi-res sourcemap for dev

[fi3ework]

Description

When developing Vite, it's very painful to find that breakpoints sometimes can't be added on some lines randomly with VS Code. Should use hi-res sourcemap to get a better debugging experience.

Tested in https://evanw.github.io/source-map-visualization/

before:

after:

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 PR Title 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.

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[bluwy]

SGTM