GH-123599: `url2pathname()`: don't call `gethostbyname()` by default (#132610)

Follow-up to 66cdb2bd8ab93a4691bead7f5d1e54e5ca6895b4.

Add *resolve_host* keyword-only argument to `url2pathname()`, defaulting to
false. When set to true, we call `socket.gethostbyname()` to resolve the
URL hostname.

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
Co-authored-by: Steve Dower <steve.dower@microsoft.com>