Builder<AddrIncoming, E> does not expose SocketAddr getter

[jonhoo]

Is your feature request related to a problem? Please describe.
I'd like to be able to get the local address that Server::bind (which returns a Builder<AddrIncoming, E>) bound to before calling Builder::serve so that I can pass the local address to the service I'm about to pass into serve.

Describe the solution you'd like
Add fn local_addr(&self) -> SocketAddr to impl Builder<AddrIncoming, E>.

Describe alternatives you've considered
Provide a way to access the full AddrIncoming via Builder, but that feels probably excessive.

Additional context
This is particularly relevant when the address passed to bind uses port 0. This comes up for me occasionally in tests where I want the test service to be aware of its own port number (to, e.g., echo back in a HTML body), which means I need to know the port before I can construct the service to pass to Builder::serve to get a Server (which does provide local_addr).

[tomkarw]

The implementation is simple, the question is whether adding a new public API to v0.14.x is worth it during v1.0 effort.

[jonhoo]

I think this can now be closed since #3278 landed?

[tomkarw]

I think Sean is waiting untill the patch with the change is realeased? Not sure what the process is.

[seanmonstar]

Oh, nope, it just doesn't auto-close become it was merged to a different branch, not master. We can close! (And I'll schedule a 0.14 release this week, cleaning through inbox.)