Else simplification pass

[DCupello1]

This pass is towards a better representation of otherwise when the only concern are boolean premises. This simply takes the original premises of the generated relations and negates them.

Example:

relation Step_pure: admininstr* ~> admininstr*
rule Step_pure/br_if-true:
  (CONST I32 c) (BR_IF l)  ~>  (BR l)
  -- if c =/= 0

rule Step_pure/br_if-false:
  (CONST I32 c) (BR_IF l)  ~>  eps
  -- otherwise

From else pass (omitting wf premises):

relation `Step_pure_before_br_if-false`: `%`(admininstr*)
  rule `br_if-true_0`{c : val_, l : labelidx}:
    `%`([CONST_admininstr(I32_valtype, c) BR_IF_admininstr(l)])
    -- if (!($proj_val__0(c))!`%`_uN.0 =/= 0)
    
relation Step_pure: `%~>%`(admininstr*, admininstr*)
  rule `br_if-true`{c : val_, l : labelidx}:
    `%~>%`([CONST_admininstr(I32_valtype, c) BR_IF_admininstr(l)], [BR_admininstr(l)])
    -- if (!($proj_val__0(c))!`%`_uN.0 =/= 0)

  rule `br_if-false`{c : val_, l : labelidx}:
    `%~>%`([CONST_admininstr(I32_valtype, c) BR_IF_admininstr(l)], [])
    -- ~ `Step_pure_before_br_if-false`: `%`([CONST_admininstr(I32_valtype, c) BR_IF_admininstr(l)])

From else simplification pass:

relation Step_pure: `%~>%`(admininstr*, admininstr*)
  rule `br_if-true`{c : val_, l : labelidx}:
    `%~>%`([CONST_admininstr(I32_valtype, c) BR_IF_admininstr(l)], [BR_admininstr(l)])
    -- if (!($proj_val__0(c))!`%`_uN.0 =/= 0)

  rule `br_if-false`{c : val_, l : labelidx}:
    `%~>%`([CONST_admininstr(I32_valtype, c) BR_IF_admininstr(l)], [])
    -- if (!($proj_val__0(c))!`%`_uN.0 = 0)

Based off of #213 , currently a draft until we iron out the details for this pass. (And modify tests)