Extend tablegen to emit builders_gen.odin -- 723 opcodes get a low-level
inst_<OpName>(buf, ...) constructor and a high-level Builder method, mapping each
grammar operand to a typed param (IdResultType->Type_Ref, IdResult->auto-allocated
Id, IdRef->Id, LiteralInteger->i64, ValueEnum/BitEnum->the typed enum, trailing
IdRef* -> []Id). builder.odin keeps just the hand-written Builder infrastructure.
Skipped (stay hand-writable, like an ISA's can_generate_builder): operands that
aren't simple typed params yet (optional, Pair* composites, LiteralString),
type-declaration opcodes (those are ir.Type), and verbs colliding with Odin
keywords/builtins (return_, switch_, size_of, ...).
Validated: a function body built via i_add / return_ encodes + round-trips
byte-exact (builder_made test) -> 10 passed.
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