[Proposal] Protobuf

I want to suggest rewriting AST into protobuf format to support it in other programming languages. Perhaps I'm not taking into account the huge amount of work that follows, but I can imagine a situation where it would be extremely useful (for example, in proto-generators for SQL interaction). Thanks for your attention!

No files, tests, or entry points are named. Start by reviewing the existing Rust AST and defining which parts would need a protobuf representation for use by other languages, including the proposed SQL interaction generators. Done would require an agreed design and an implementation plan, rather than a small isolated change.

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