b341e59f10
Living under `layout` at least for now, since it lacks a lot of functionalities that, say, `mozilla::UniquePtr` has. This is in preparation for optimizing `AnchorResolved<T>` in bug 1960032, which will be addressing the perf regression in bug 1959134. See comment 3 for further context. Differential Revision: https://phabricator.services.mozilla.com/D246229