Allow local references in addition to fully qualified ones in types and values

[AttilaMihaly]

Discussed in #220

Multiple community members brought up the wish to handle smaller portions of the IR as independent units instead of always working with an entire distribution. While the IR is very composable and you can independently define individual types or functions one specific design choice makes that less feasible:

The fact that we use fully qualified names in every reference (types, values, constructors) means that even when you are looking at a single definition you still need to be aware of the whole IR structure when you are trying to resolve a reference even if it is local.

To fix this we can introduce a new type:

module Morphir.IR.Ref exposing (..)

type Ref
    = ModuleLocalRef Name
    | PackageLocalRef QName
    | GlobalRef FQName

Then we can replace FQName in Reference in both places:

module Morphir.IR.Type exposing (..)

type Type a
    = ...
    | Reference a Ref (List (Type a))
    | ...

module Morphir.IR.Value exposing (..)

type Value ta va
    = ...
    | Constructor va Ref
    | Reference va Ref
    | ...