Migrate from tsup -> tsdown -> vp pack

[TheAlexLichter]

Description

As a dev with legacy apps I'd appreciate taking tsup into consideration as a migration target when moving a lib to vite+ via vp migrate

Suggested solution

Migrate this for me (similar to oxlint migrate or oxfmt).

Alternative

Do it manually.

Additional context

No response

Validations

• Read the Contributing Guidelines.
• Confirm this request is for Vite+ itself and not for Vite, Vitest, tsdown, Rolldown, or Oxc.
• Check that there isn't already an issue requesting the same feature.