Add new HelperInstr sort

[anvacaru]

• Introduced a new HelperInstr sort in WASM-INTERNAL-SYNTAX for existing auxiliary Instr productions.
• Moved all internal execution-phase instruction productions out of into HelperInstr subsort:
  • covering control flow (#block, #br, #if, #loop),
  • variable access (#local.*, #global.*),
  • table operations (#table.*, #tableGet, #tableFill),
  • reference instructions (#ref.is_null, #ref.func),
  • call helpers (#call, #callIndirect),
  • memory stepping helpers (grow, fill, copy, fillTrap, copyTrap),
  • local initialization (init_local, init_locals).

[bbyalcinkaya]

Looks good overall. Thank you! Approving with some change requests. Please apply them before merging.

A few actual Wasm instructions seem to have been moved into HelperInstr. I’ve suggested inline fixes for these.

A practical rule of thumb, if an Instr production has a symbol attribute, it is likely a real Wasm instruction and should remain under Instr. These symbols are used by the binary parser when constructing Wasm ASTs.