cleanup: netx does not use netxlite legacy names (#801)

This diff refactors netx and netxlite to ensure we're not using
netxlite legacy names inside of netx.

To this end, we're cheating a bit. We're exposing a new factory to
get an unwrapped stdlib resolver rather than defining a legacy name
to export the private name of the same factory.

This is actually a fine place to stop, for now, the next and
netxlite refactoring at https://github.com/ooni/probe/issues/2121.

internal/netxlite/dialer.go

@@ -15,10 +15,10 @@ import (
 )
 
 // NewDialerWithStdlibResolver is equivalent to creating a system resolver
-// using NewResolverStdlib and then a dialer using NewDialerWithResolver where
+// using NewStdlibResolver and then a dialer using NewDialerWithResolver where
 // the resolver argument is the previously created resolver.
 func NewDialerWithStdlibResolver(dl model.DebugLogger) model.Dialer {
-	reso := NewResolverStdlib(dl)
+	reso := NewStdlibResolver(dl)
 	return NewDialerWithResolver(dl, reso)
 }