Fix int/float coercion according to the execution algo

[JoviDeCroock]

Resolves #4488

This is kind of ... hard to assess where to best put this. I've put it in the scalar serialize as it felt the most appropriate, we could also put it in completeValue and return null regardless of whether this is an int/float scalar. We should however not throw errors so instead we'd return NaN from the scalars then instead of null and catch that in completeValue.

I found it a bit awkward to disregard the value completely for other types so I opted to put it in the scalars for that reason, i.e. there could be legitimate use cases for test-results or others where N/A is different from null.

We are sacrificing some form of accuracy here as a non-nullable field will return "cannot return null for x" when NaN is supplied while we do become more accurate by returning null for a nullable field rather than an error.