[vite plugin] allow resolving unenv aliases to packages

[vicb]

Sometimes unenv aliases can point to packages.

For example the base unenv package aliases debug to a shim /unenv/....
But we want to use the actual package instead, so we override that by creating an alias debug -> debug.

Before this PR, the plugin assumed that the alias as to be a path and it would throw when trying to resolve the debug path.
This PR updates the plugin so that it assumes that the alias is a package when it can not be resolved to a path.

This was tested on top of #11079 and solves the test issues there.

---

• Tests
  • Tests included
  • Tests not necessary because: tested manuallu, merging 11079 will test that (see details above)
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: fix
• Wrangler V3 Backport
  • Wrangler PR:
  • Not necessary because: unenv changes are not backported to v3

[changeset-bot]

🦋 Changeset detected

Latest commit: 623549b

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commit: 623549b

[jamesopstad]

Thanks @vicb.