fix: rework lazily remote function files discovery

[dummdidumm]

Instead of using manualChunks which turns out to cause some weird chunking bugs, we instead use a virtual module which we force to be loaded at the very end after all other modules have been discovered. By that time we have collected all remote function files and can generated a record of hash->import. Vite will then do the proper chunking without further interference by us. Thanks @bluwy for the tip!

Fixes #14444 and possibly #14430

Putting this into draft because while working on this I discovered that remote functions in node_modules are not loaded at dev time - but this is not new to this PR, it's failing on main, too. Investigating.

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