Function tor_circmgr::build::create_common

async fn create_common<RT: Runtime, CT: ChanTarget>(
    chanmgr: &ChanMgr<RT>,
    rt: &RT,
    target: &CT,
    guard_status: &GuardStatusHandle,
    usage: ChannelUsage
) -> Result<PendingClientCirc>

Try to make a [PendingClientCirc] to a given relay, and start its reactor.

This is common code, shared by all the first-hop functions in the implementation of Buildable for Arc<ClientCirc>.