Performance/Detect does not work with [0] or [-1]

## Is your feature request related to a problem? Please describe.

Since for arrays `[0]` is usually the same as `.first` and `[-1]` is same as `.last` I would expect the `Performance/Detect` to identify performance problems with index syntax as well.

## Describe the solution you'd like

Add index syntax to  `Performance/Detect` cop
