* No longer emit div_exact AIR instruction that can produce a
   remainder, invoking undefined behavior.
 * div_trunc, div_exact, div_floor are extracted from analyzeArithmetic
   and directly handled similarly to div_trunc, integrating them with
   integer overflow safety checking.
 * Also they no longer emit divide-by-zero safety checking when RHS
   is comptime known to be non-zero.