feat: Allow external remote functions to be whitelisted

[ottomated]

fixes #13979

Adds a new config option, remoteFunctions.allowedPaths, which allows remote functions to be loaded outside of $lib and routes.

• Adds a nice warning when a user attempts to import remote functions that aren't whitelisted
• Adds a test for the above (couldn't figure out how to test console output in playwright, if that's possible)

Also, if there's a better way to give the vite plugin access to manifest_data at dev time, let me know.

cc @dummdidumm

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[ottomated]

Maybe return a shim module that throws a error when imported here, rather than allow the 404?