unused_enumerated rule should also check closure parameters

[SimplyDanny]

The unused_enumerated rule triggers when either of the two values returned by .enumerated() isn't used (replaced by an underscore _). The rule currently checks only for loops. It could be extended to support closure parameters as well.

The rule would only check the immediate closure after the .enumerated() call. Otherwise, the number of parameters and their types could have changed.

Triggering:

list.enumerated().map { idx, _ in idx }

list.enumerated().map { _, elem in elem }

list.enumerated().forEach { print($0) }

list.enumerated().map { $1 }

Non-triggering:

list.enumerated().map { idx, elem in "\(idx): \(elem)" }

list.enumerated().map { $0 + $1 }

list.enumerated().something().map { _, elem in elem }

PS: This enhancement was motivated by this comment.

[mildm8nnered]

I am playing around with some fixes for this ...