implement `TrustedRandomAccess` for `Take` iterator adapter
`TrustedRandomAccess` requires the iterator length to fit within `usize`. `take(n)` only constrains the upper bound of an iterator. So if the inner is `TrustedRandomAccess` (which already implies a finite length) then so can be `Take`.
```````@rustbot``````` label T-libs-impl
c00439f682