Lowering: Atomic ops can produce a value (#19173)

Lowering: Atomic ops can produce a value (#19173)

* Lowering: Atomic ops can produce a value

#18887 changed OperIsStore to include the atomic functions, but `Lowering::LowerArg()` and `Lowering::CheckCallArg()` assume that stores do not produce a value, so it doesn't correctly set the argument register (or build a `PUTARG_REG`) for the case where the result of an atomic op is passed to a call.
Fix this and add additional asserts.

Fix #19171