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/measurex/tracing.go

@@ -54,7 +54,7 @@ func NewTracingHTTPTransport(logger model.Logger, begin time.Time, db WritableDB
 func NewTracingHTTPTransportWithDefaultSettings(
 	begin time.Time, logger model.Logger, db WritableDB) *HTTPTransportDB {
 	return NewTracingHTTPTransport(logger, begin, db,
-		netxlite.NewResolverStdlib(logger),
+		netxlite.NewStdlibResolver(logger),
 		netxlite.NewDialerWithoutResolver(logger),
 		netxlite.NewTLSHandshakerStdlib(logger),
 		DefaultHTTPMaxBodySnapshotSize)