Rollup merge of #125551 - clarfonthey:ip-bits, r=jhpratt

Stabilise `IpvNAddr::{BITS, to_bits, from_bits}` (`ip_bits`)

This completed FCP in #113744. (Closes #113744.)

Stabilises the following APIs:

```rust
impl Ipv4Addr {
    pub const BITS: u32 = 32;
    pub const fn from_bits(bits: u32) -> Ipv4Addr;
    pub const fn to_bits(self) -> u32;
}

impl Ipv6Addr {
    pub const BITS: u32 = 128;
    pub const fn from_bits(bits: u128) -> Ipv4Addr;
    pub const fn to_bits(self) -> u128;
}
```

library/core/src/lib.rs

@@ -174,7 +174,6 @@
 #![feature(duration_consts_float)]
 #![feature(internal_impls_macro)]
 #![feature(ip)]
-#![feature(ip_bits)]
 #![feature(is_ascii_octdigit)]
 #![feature(isqrt)]
 #![feature(link_cfg)]