Rewrite the builder generator to cover every opcode -- each operand maps to a
typed param by kind + quantifier, emitted with a running operand index so all
shapes compose:
optional '?' -> Maybe(T)
variadic '*' -> []T
composite Pair* -> []Pair_Id_Id / []Pair_Lit_Id / []Pair_Id_Lit
LiteralString -> string (packed into word operands)
Id/Lit/enum -> Id / i64 / the typed enum (ValueEnum) or bit_set (BitEnum)
A verb that would clash with an Odin keyword, builtin, builtin type name, or a
re-exported ir.type_* constructor gets a trailing '_' (return_, switch_, string_,
size_of_, type_void_, ...). builder.odin gains the Pair_* types + a string packer.
873 inst_<OpName> + 873 Builder methods. Package compiles; suite 10 passed.