0518ecc700
Stabilize (const_)slice_ptr_len and (const_)slice_ptr_is_empty_nonnull
Stabilized API:
```rust
impl<T> *mut [T] {
pub const fn len(self) -> usize;
pub const fn is_empty(self) -> bool;
}
impl<T> *const [T] {
pub const fn len(self) -> usize;
pub const fn is_empty(self) -> bool;
}
impl<T> NonNull<[T]> {
pub const fn is_empty(self) -> bool;
}
```
FCP completed in tracking issue: https://github.com/rust-lang/rust/issues/71146