PAC with collisions

[RemyCiterin]

This PR extend the previous PR I did for Pointer Authentication Code to add the support for hash collisions, for example a program like this one:

AArch64 Simple Collision
Variant=pac,fpac
{ 0:X0=x }
P0                  ;
  PACDZA X0 ;
  AUTDZB X0;
exists ( ~Fault(P0) )

may run without fault because of a hash collision between pacda(x,0) and pacdb(x,0). But this program:

AArch64 Collision contradiction
Variant=pac,fpac
{ 0:X0=x; 0:X1=x;; }
P0;
  PACDZA X1   ;
  PACDZB X0   ;
  CMP X0,X1   ;
  B.EQ finish ;
  AUTDZA X0   ;
  MOV X2,#1   ;
finish:       ;
exists (~Fault(P0) /\ 0:X2=1)

can't return without fault and 0:X2=1 because otherwise their is a contradiction about the same collision. And herd will return (ideally with some debug flags because this output is not possible in litmus):

Test Collision Allowed
States 2
0:X2=0;  ~Fault(P0); pacda(x, 0x0)=pacdb(x, 0x0);
0:X2=0; Fault(P0,PacCheck:DA);
No
Witnesses
Positive: 0 Negative: 2
Condition exists (not (fault(P0)) /\ 0:X2=1)
Observation Collision Never 0 2
Time Collision 0.01
Hash=e743d111643250ebd8d3bb2a4c991cf9

This PR is till not 100% finish, I still have some update to do, as example: ensure that the pretty printing by default is the same between herd and litmus like I did for the version without collisions, moving the docs from pac_tests...