[Eva] Changes the signature of the widening in most cvalue modules.

- In int_interval, int_val, ival, locations and cvalue: [widen] now takes
  optional named arguments [size] and [hint].
- Updates Offsetmap functor accordingly.
- Removes types [numerical_widen_hint] and [size_widen_hint]:
  modules only declare one [widen_hint] type.
- Removes module Ival.Widen_hints, and uses Integer.Set directly instead.