[Eva] Results: exports new function to evaluate the taint of a memory zone.

In the taint domain:
- exports generic function [is_tainted] evaluating the taint of a memory zone
  in a given state. Removes function [is_tainted_property].
- returns Direct/Indirect/Untainted instead of Data/Control/None.

Implements [is_tainted_property] in the general request,
using [Results.is_tainted].