Introduce UpdateField trait to generalize field transformation in partial data

[soareschen]

Summary

This PR introduces a new UpdateField trait that generalizes the update operation for partial record fields:

pub trait UpdateField<Tag, M: MapType> {
    type Value;

    type Mapper: MapType;

    type Output;

    fn update_field(
        self,
        _tag: PhantomData<Tag>,
        value: M::Map<Self::Value>,
    ) -> (<Self::Mapper as MapType>::Map<Self::Value>, Self::Output);
}

This generalizes the field update operations of inserting field values or taking out field values. With this, traits like BuildField, TakeField, and TransformMapFields can be implemented as blanket implementations on UpdateField, instead of being derived explicitly by the proc macros.