Conversion of Flow types to Tetra types This only handles the subset of flow that occurs after lowering.
Convert types from Flow to Tetra.
The majority of type conversions are just replacing one name with another,
so these are performed in
Others require removing arguments or adding regions are performed here, before name conversion:
* Rate foralls are removed
Series k a becomes
Ptr# rTop a
RateNat k becomes
Ref a becomes
Ref# rTop a
a -> b -> S (Read rT + Write rT + Alloc rT) c