Implement `PartialEq` for RunArray

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
As @brancz and I found on #7649 (comment), unlike other arrays like `PrimitiveArray

That means we couldn't compare them like

let arr1 = RunArray::new...
let arr2 = RunArray::new...
assert_eq!(arr1, arr2);

Describe the solution you'd like
I would like to be able to compare 2 run arrays using ==

Describe alternatives you've considered

Additional context

[brancz]

Opened #7727