Modify heuristic for floating handle bodies
Modify heuristic for floating handle bodies

- Constructors don't need to be floated to a named definition, even if
  not nullary. We must allow them later because literals turn into
  unary constructors.
- Applications of a function variable are structured. Only constructor
  applications may be considered unstructured.
- Constructor applications may be locally floated out of a handle during
  ANF, because they don't incur any effects.

unisonweb/platform,unisonweb/platform,unisonweb/platform