--- In the case of @newtype@s, it returns one of:
---
--- 1) A vanilla 'TyConApp' (recursive newtype, or non-saturated)
---
--- 2) The newtype representation (otherwise), meaning the
--- type written in the RHS of the newtype declaration,
--- which may itself be a newtype
---
--- For example, with:
---
--- > newtype R = MkR S
--- > newtype S = MkS T
--- > newtype T = MkT (T -> T)
---
--- 'expandNewTcApp' on:
---
--- * @R@ gives @Just S@
--- * @S@ gives @Just T@
--- * @T@ gives @Nothing@ (no expansion)
-