Add List.getOrNull()

[windrunner414]

add a extension function getOrNull(int index) on List to get element at the specified index safely. If out of bounds, return null.
It can work well with nnbd.

ref: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/get-or-null.html

[alexeyinkin]

This should be on Iterable since elementAt is there. Also it might be named elementAtOrNull for consistency.

[lrhn]

No current plans to treat index errors as acceptable in lists. Don't expect that to change. It's very easy to do a list.length check first, rather than have a function that silently ignores out-of-bound accesses.

For iterable, it makes more sense ... but annoyingly an operation on iterable will work for List too.
Still, I'd prefer something cleaner, not null based, like Option<T> tryElementAt(int index) that would return a recognizable non-value if index is too big. (And it'll still throw for negative indices.)