refactor: i/errorsx is now i/legacy/errorsx (#479)

We need still to add similar wrappers to internal/netxlite but we
will adopt a saner approach to error wrapping this time.

See https://github.com/ooni/probe/issues/1591

internal/engine/legacy/errorsx/tls_test.go

@@ -0,0 +1,43 @@
+package errorsx
+
+import (
+	"context"
+	"crypto/tls"
+	"errors"
+	"io"
+	"net"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/netxlite/errorsx"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/mocks"
+)
+
+func TestErrorWrapperTLSHandshakerFailure(t *testing.T) {
+	th := ErrorWrapperTLSHandshaker{TLSHandshaker: &mocks.TLSHandshaker{
+		MockHandshake: func(ctx context.Context, conn net.Conn, config *tls.Config) (net.Conn, tls.ConnectionState, error) {
+			return nil, tls.ConnectionState{}, io.EOF
+		},
+	}}
+	conn, _, err := th.Handshake(
+		context.Background(), &mocks.Conn{
+			MockRead: func(b []byte) (int, error) {
+				return 0, io.EOF
+			},
+		}, new(tls.Config))
+	if !errors.Is(err, io.EOF) {
+		t.Fatal("not the error that we expected")
+	}
+	if conn != nil {
+		t.Fatal("expected nil con here")
+	}
+	var errWrapper *errorsx.ErrWrapper
+	if !errors.As(err, &errWrapper) {
+		t.Fatal("cannot cast to ErrWrapper")
+	}
+	if errWrapper.Failure != errorsx.FailureEOFError {
+		t.Fatal("unexpected Failure")
+	}
+	if errWrapper.Operation != errorsx.TLSHandshakeOperation {
+		t.Fatal("unexpected Operation")
+	}
+}