Make the IR typed

[LPTK]

TODOs:

• Q (separate PR): Can we split the IR's Ref into

    // case Ref(l: Local, disamb: Opt[DefinitionSymbol[?]])
    case Ref(l: LocalSymbol)
    case MemberRef(l: BlockMemberSymbol, disamb: DefinitionSymbol[?])

  Note: first (before refactoring), we can try to check the invariant at runtime, and if it holds, we should be able to do it
• Define ErasedType – for now, just have case AnyRef(rsc: Bool, csym: ClassLikeSymol) and case Primitive(‹things like i31›)
• For now, we add an ErasedType field to the symbols that represent values; it starts out as absent and will be populated by the resolution process. When absent, we just assime Object (ie AnyRef(false, ObjectSymol)).
• Add resultType: ErasedType to functions
• Add a pass of explicit coercions/unboxing, allowing to produce WASM that doesn't treat everything as anyref

Eventual goal: use this to compile resources (using refcounting).

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Original items (probably won't do for now):

• Define ErasedType – for now, just have case Object (top), case AnyRef(rsc: Bool), case Union(Ls[ErasedType]) and case Primitive(‹things like i31›)
• Make params: Ls[BlockParamList] in functions
• Change Ref, MemberRef, and Select wrap their symbol inside a new symbol kind BlockSymbol which includes an ErasedType