Starting in iOS 7, Apple added a built-in basic barcode scanning with AV Foundation.
Does Android 5 or 6 (or any future version) have anything similar?
Just something basic like UPC, EAN, QR code, etc.
Android does not, but the Google Play Services Vision API does.
To use it, you will need to add the Google Play Services SDK as a dependency in your app, and the end-user will need Google Play Services and Android 4.2.2 or newer installed on their device.
The Vision API currently supports the following formats