[Feature Request] Relax Lint/ComparisonToBoolean to allow unions with Bool

[HertzDevil]

Comparisons to booleans are not pointless if the other operand is a union containing Bool:

def f(x : Int32 | Bool)
  print 1 if x == true
  print 2 if x == false
  print 3 if x
  print 4 if !x
  puts
end

f(0)     # 3
f(true)  # 13
f(false) # 24

(Comparisons to unions not containing Bool are still pointless, as they should always evaluate to false.)

[veelenga]

In Crystal comparison to booleans can be used to narrow down the type of the variable, thus doing the static analysis, we are not able to properly handle this. Refs #12

def f(x: Bool | Nil)
  if x == false
    # x is not Int32 and not Nil here.
  end
end