fix(app-vite): local import of extensions in windows

[lvf23]

• Possibly fix the issue documented here:

"There have been many reports of problems linking via file: and link:. This is outside of Quasar’s reach, but is likely to do with your development environment, aka your mileage with Windows will vary."

https://quasar.dev/app-extensions/development-guide/introduction#manually-testing

• Now it's possible to load Quasar App Extensions without host in platforms like Github, Gitlab, etc.

• Fix errors like for local Quasar App Extension:

App • ⚠️ App Extension "[ext-name]" has missing index script...

• Tested in Windows 10 with local Quasar App Extension

What kind of change does this PR introduce?

• Bugfix
• Refactor
• Feature
• Documentation
• Code style update
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the dev branch (or v[X] branch)
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)
• It's been tested on a Cordova (iOS, Android) app
• It's been tested on an Electron app
• Any necessary documentation has been added or updated in the docs or explained in the PR's description.

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to start a new feature discussion first and wait for approval before working on it)

Other information:

Any adaptation needed do not hesitate to call me. I could adjust it or give more feedback. Feel free to edit according to the better fit for the project.