Remove "specifier" on Range when able or don't use Range

[dsherret]

specifier on Range is largely duplicate information that can already be found based on what module someone is in. We should try to not store it when able.

Also, we should probably remove the specifier property on Range because that's duplicate information that can be figured out by looking at the current module's specifier.

#247 (comment)

• Also, as part of this, Resolver's referrer_range's position should be made optional.