Default name for reference variants

[timothee-haudebourg]

A common pattern in TreeLDR is to declare a union layout of the form:

Foo | &Foo

This represents a layout with two variants, either Foo or a reference to Foo. In TreeLDR, all the variants must be named. When possible a default name is given, corresponding to the name of the variant layout. However reference layouts have no names, so the previous layout must be rewritten as:

Foo | &Foo as FooRef

Since this is a common pattern, a default name should be given to the reference variant in this situation following the convention <ReferencedTypeName>Ref.