fix: disable fsServe restrictions by default

[antfu]

Description

As discussions with the team, we decided to postpone the fsServe restrictions to v2.4.0 or later when we find the solutions to solve a few issues and make the logic more robust and well tested.

This PR adding a new options server.fsServe.strict and set the default to false, and disabling the restrictions by default. In the future versions of Vite, we will change server.fsServe.strict to true when the restrictions issue are resolved.

You can still opt-in this security change by

export default {
  server: {
    fsServe: {
      strict: true
    }
  }
}

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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