* 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`.
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