[freeciv-ai] (PR#3584) Renaming vulnerability/belligerence

["Gregory Berkolaiko" <Gregory.Berkolaiko@xxxxxxxxxxxx>]

I am planning to rename the travesty that is unit_vulnerability and
unit_belligerence functions.  The present naming is a disgrace.  There
is also a bug of missed firepower.  My proposition for the new names is
below.

Please voice your objections now.

G.

Renaming:
=========
1. base_unit_belligerence_primitive
  -> unittype_att_rating
2. unit_belligerence_basic
  -> unit_att_rating
3. unit_belligerence_primitive
  -> unit_att_rating_now
4. unit_belligerence
  -> unit_att_rating_sq


Editing:
========
1. unit_vulnerability_virtual must be multiplied by firepower!
2. Remove alternativ_hp from unit_vulnerability_virtual2
  (not used).


More renaming:
==============
1. unit_vulnerability_virtual2
  -> unittype_def_rating_sq
2. unit_vulnerability_virtual
  -> unit_def_rating_basic_sq
3. unit_vulnerability_basic
  -> unit_def_rating
4. unit_vulnerability
  -> unit_def_rating_sq


Add:
====
1. unit_def_rating_basic  and make 
unit_def_rating_basic_sq it's square.