Add `From` impls for wrapper types - ~`From<T: Copy> for ManuallyDrop<T>`~ - `From<T: UnwindSafe> for AssertUnwindSafe<T>` - `From<T> for LazyCell<T, F>` - `From<T> for LazyLock<T, F>` - `From<T> for ThinBox<T>` (unstable) - `From<T> for UniqueRc<T>` (unstable) - `From<T> for UniqueArc<T>` (unstable) @rustbot label T-libs-api needs-fcp Also needs a crater run, as the insta-stable impls are technically breaking changes.