Unified reference 'setting' API

[kaleidawave]

Envisioning a Reference enum (rename existing Reference from events to RootReference) that is a enum Reference { Variable(VariableId), Property { on: TypeId, key: TypeId } }. The there could be a set_reference method on Context that is the following.

fn set_reference<T: crate::FSResolver, U: Operator>(
   &mut self,
   reference: Reference,
   operation: U,
   rhs: &U::RHS,
   checking_data: &mut CheckingData<T>
) -> TypeId

Where Operator is the following

trait Operator {
    type RHS: SynthesiseToType;

    fn return_behavior(&self) -> ReturnBehavior;
}

trait SynthesiseToType {
    fn to_type(&self, ...) -> TypeId;
}

enum ReturnBehavior {
    NewValue,
    OldValue
}

This would handle all the update/assignment operations and (hopefully) be the simplest way to add this.

[kaleidawave]

This was completed in #31