* introduce float_to_int and int_to_float AIR instructionts and
   implement for the LLVM backend and C backend.
 * Sema: implement `zirIntToFloat`.
 * Sema: implement `@atomicRmw` comptime evaluation
   - introduce `storePtrVal` for when one needs to store a Value to a
     pointer which is a Value, and assert it happens at comptime.
 * Value: introduce new functionality:
   - intToFloat
   - numberAddWrap
   - numberSubWrap
   - numberMax
   - numberMin
   - bitwiseAnd
   - bitwiseNand (not implemented yet)
   - bitwiseOr
   - bitwiseXor
 * Sema: hook up `zirBitwise` to the new Value bitwise implementations
 * Type: rename `isFloat` to `isRuntimeFloat` because it returns `false`
   for `comptime_float`.