Auto merge of #75212 - JulianKnodt:array_map, r=LukasKalbertodt

Auto merge of #75212 - JulianKnodt:array_map, r=LukasKalbertodt

Add `array` lang item and `[T; N]::map(f: FnMut(T) -> S)`

This introduces an `array` lang item so functions can be defined on top of `[T; N]`. This was previously not done because const-generics was not complete enough to allow for this. Now it is in a state that is usable enough to start adding functions.

The function added is a monadic (I think?) map from `[T; N] -> [S; N]`. Until transmute can function on arrays, it also allocates an extra temporary array, but this can be removed at some point.

r? @lcnr