System.Index indexing for arrays does not use pattern-based Index

[agocke]

https://sharplab.io/#v2:EYLgtghgzgLgpgJwDQxASwDYB8ACAmARgFgAoHABgAIcCAWAblNJwGZq9KBhS0gb1MqDqBAGyU0AOxiUAsgApJMANoBdShAQIAlEMEBeAHzrNSgHoEV9SgHprlAO4ALAJ4B+AUI+CaYgMaONWTkaKlhtIUNKMLMLRhJdL2ExRSCAZQAHCAkAHkUjKHSJHUiCiRjLRIT4oR9xKSCAGTRYXKkjDFhi9thyuIBfIA==

[alrz]

we can save up a few locals as well, index doesn't need to be captured in a local if it's not sideeffecting, I think we have a helper for that.