Add new Style/NegatedIfElseCondition cop

[fatkodima]

This cop checks for uses of if-else and ternary operators with a negated condition which can be simplified by inverting condition and swapping branches.

# bad
if !x
  do_something
else
  do_something_else
end

# good
if x
  do_something_else
else
  do_something
end
      
# bad
!x ? do_something : do_something_else

# good
x ? do_something_else : do_something

# bad 
if x != y
  do_something
else
  do_something_else
end

# good
if x == y
  do_something_else
else
  do_something
end

I'm sure, there is a better name for this cop.

[bbatsov]

negative -> negated

and what the conditional's branches (or something like this)

[bbatsov]

Nicely done! I only had a tiny bit of feedback about the message. I'm also thinking a better name for the cop might be "NegatedIfElseCondition".

[fatkodima]

Changed the cop name and offense message.

[bbatsov]

Thanks!