Rollup merge of #130629 - Dirbaio:net-from-octets, r=tgross35

core/net: add Ipv[46]Addr::from_octets, Ipv6Addr::from_segments.

Adds:

- `Ipv4Address::from_octets([u8;4])`
- `Ipv6Address::from_octets([u8;16])`
- `Ipv6Address::from_segments([u16;8])`

equivalent to the existing `From` impls.

Advantages:

- Consistent with `to_bits, from_bits`.
- More discoverable than the `From` impls.
- Helps with type inference: it's common to want to convert byte slices to IP addrs. If you try this

```rust
fn foo(x: &[u8]) -> Ipv4Addr {
   Ipv4Addr::from(foo.try_into().unwrap())
}
```

it [doesn't work](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=0e2873312de275a58fa6e33d1b213bec). You have to write `Ipv4Addr::from(<[u8;4]>::try_from(x).unwrap())` instead, which is not great. With `from_octets` it is able to infer the right types.

Found this while porting [smoltcp](https://github.com/smoltcp-rs/smoltcp/) from its own IP address types to the `core::net` types.

~~Tracking issues #27709 #76205~~
Tracking issue: https://github.com/rust-lang/rust/issues/131360

library/core/tests/lib.rs

@@ -50,6 +50,7 @@
 #![feature(hashmap_internals)]
 #![feature(int_roundings)]
 #![feature(ip)]
+#![feature(ip_from)]
 #![feature(is_ascii_octdigit)]
 #![feature(isqrt)]
 #![feature(iter_advance_by)]