[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!

未指定任何文件、测试或入口点。首先检查现有的 Rust AST，并确定哪些部分需要提供 protobuf 表示，以供其他语言使用，其中包括拟议的 SQL 交互生成器。完成的要求应是达成一致的设计和实施计划，而不是一个小型的孤立改动。

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