Introduction of Yoda condition checking.

This PR aims to implement [realm#1924][1].
[1]: realm#1924 (+1 squashed commit)
Squashed commits:
[b6a5af92] Updates changelog entry

Moves entry to new section.

CHANGELOG.md

@@ -84,10 +84,6 @@
   [JP Simard](https://github.com/jpsim)
   [#1822](https://github.com/realm/SwiftLint/issues/1822)
 
-* Add `private_action` opt-in rule which warns agaist public @IBAction methods.  
-  [Ornithologist Coder](https://github.com/ornithocoder)
-  [#1931](https://github.com/realm/SwiftLint/issues/1931)
-
 ##### Bug Fixes
 
 * Extend `first_where` and `contains_over_first_not_nil` rules to also detect