Rollup merge of #115955 - tgross35:ip-to-canonical, r=dtolnay

Stabilize `{IpAddr, Ipv6Addr}::to_canonical`

Make `IpAddr::to_canonical` and `IpV6Addr::to_canonical` stable (+const), as well as const stabilize `Ipv6Addr::to_ipv4_mapped`.

Newly stable API:

```rust
impl IpAddr {
    // Newly stable under `ip_to_canonical`
    const fn to_canonical(&self) -> IpAddr;
}

impl Ipv6Addr {
    // Newly stable under `ip_to_canonical`
    const fn to_canonical(&self) -> IpAddr;

    // Already stable, this makes it const stable under
    // `const_ipv6_to_ipv4_mapped`
    const fn to_ipv4_mapped(&self) -> Option<Ipv4Addr>
}
```

These stabilize a subset of the following tracking issues:

- https://github.com/rust-lang/rust/issues/27709
- https://github.com/rust-lang/rust/issues/76205

Stabilization of all methods under the `ip` gate was attempted once at https://github.com/rust-lang/rust/pull/66584 then again at https://github.com/rust-lang/rust/pull/76098. These were not successful because there are still unknowns about `is_documentation` `is_benchmarking` and similar; `to_canonical` is much more straightforward.

I have looked and could not find any known issues with `to_canonical`. These were added in 2021 in https://github.com/rust-lang/rust/pull/87708

cc implementor ``@the8472``

r? libs-api
``@rustbot`` label +T-libs-api +needs-fcp

0 files changed, 0 insertions, 0 deletions