refactor(bridge): align bridge with vite and inline systemjs polyfill in entry

[danielroe]

🔗 Linked issue

resolves nuxt/bridge#129

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR:

1. makes bridge + vite-builder more closely aligned, including porting support for dynamic base paths to bridge vite, including using untyped to give us just the vite default options
2. inlines systemjs polyfill for now (otherwise it was susceptible to a race condition and possibly not being loaded - note that this is a temporary fix and we will remove legacy support in bridge: Serve modern format with bridge and vite bridge#15

A lingering issue is that Bridge does not respect static URLs in terms of custom baseURL or cdnURL - this can be deferred to another PR.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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