Performance/ReverseEach only captures array literals

[dvandersluis]

Performance/ReverseEach only catches offenses if the receiver of reverse.each is an array literal. If the receiver is a variable or a method call, it does not match the node and does not register an offense.

I would be happy to contribute a PR to fix this, but I'm not sure how to detect what receivers this should apply to. If it's okay to apply this cop to any receiver, I have a fix ready to go, but I'm not sure how to detect that the receiver is an Enumerable (if that's even possible).

---

Expected behavior

Neither of these examples are picked up by the cop:

arr = [1, 2, 3]
arr.reverse.each

def arr
  [1, 2, 3]
end

arr.reverse.each

Actual behavior

Neither of the above examples register offenses.

Steps to reproduce the problem

Both of the above examples reproduce the problem.

RuboCop version

$ rubocop -V
0.55.0 (using Parser 2.5.1.0, running on ruby 2.4.3 x86_64-darwin16)