docs(standard): add `nodiscard` to immutable array functions

Summary

Some functions are expecting the return value to be used, as they should have no side effects themselves as being immuntable. Add nodiscard to these functions allows to faster spot potential bugs in the code (such as was seen with #4183)

How did you test this change?

tested by hjp

Done the fixes, but not tested, would be great is someone could

tested (via previews) on dota, lol, brawlstars, valorant, wildrift, overwatch and stormgate

Given most of the changes happen to Array.mapIndexes, would it make sense to add a second version of that, e.g. forEachIndexed or something, which would not return anything? Iterating a second time shouldn't really be necessary, no? Otherwise, does local _ = Array.mapIndexes also silence the errors?

I agree that some new function would be better, and have it stop when an iteration returns false/nil (or continue until they stop returning a true?). Not sure what a good name would be though. forEachIndexed. Maybe just call it for and have optional(?) params which are starting and ending indexed that default to 1 and math.huge? So it would just be a for index = startIndex, endIndex do loop but in a function. Or we could just use for index = 1, math.huge do instead :p

I agree that some new function would be better, and have it stop when an iteration returns false/nil (or continue until they stop returning a true?). Not sure what a good name would be though. forEachIndexed. Maybe just call it for and have optional(?) params which are starting and ending indexed that default to 1 and math.huge? So it would just be a for index = startIndex, endIndex do loop but in a function. Or we could just use for index = 1, math.huge do instead :p

Blame me for not looking up what the function actually does. Nontheless, it looks like all the usages shown in this PR aren't the intended use case