Extend the tablegen to emit encoding_table.odin from the grammar -- the
per-opcode operand layout that drives the codec:
INSTRUCTION_SPECS flat []Operand_Spec {Spec_Kind, Quantifier}
INSTRUCTION_INDEX [max_opcode+1]Spec_Run -- O(1) opcode -> its operand run
ENUM_PARAMS enumerant -> trailing-parameter operands, so the codec
PARAM_SPECS reads MemoryAccess.Aligned / OpExecutionMode LocalSize /
Decoration.SpecId etc. correctly
873 opcodes, 3693 operand specs. Package compiles.