Auto merge of #33976 - komamitsu:assert_eq_with_msg, r=alexcrichton

Add custom message parameter to `assert_eq!`

`assert!` macro accepts a custom message parameter and it's sometimes useful. But `assert_eq!` doesn't have it and users need to use `assert!` instead of `assert_eq!` when they want to output a custom message even if the assertion just compares two values. This pull request will resolve those cases.