refactor: move ErrorWrapperQUICDialer to errorsx (#420)

I needed to add some tests as integration tests due to circular
imports, but this is ~fine because we quite likely want many
integration tests in the errorsx package anyway.

Part of https://github.com/ooni/probe/issues/1505.

internal/errorsx/quic.go

@@ -0,0 +1,38 @@
+package errorsx
+
+import (
+	"context"
+	"crypto/tls"
+
+	"github.com/lucas-clemente/quic-go"
+)
+
+// QUICContextDialer is a dialer for QUIC using Context.
+type QUICContextDialer interface {
+	// DialContext establishes a new QUIC session using the given
+	// network and address. The tlsConfig and the quicConfig arguments
+	// MUST NOT be nil. Returns either the session or an error.
+	DialContext(ctx context.Context, network, address string,
+		tlsConfig *tls.Config, quicConfig *quic.Config) (quic.EarlySession, error)
+}
+
+// ErrorWrapperQUICDialer is a dialer that performs quic err wrapping
+type ErrorWrapperQUICDialer struct {
+	Dialer QUICContextDialer
+}
+
+// DialContext implements ContextDialer.DialContext
+func (d *ErrorWrapperQUICDialer) DialContext(
+	ctx context.Context, network string, host string,
+	tlsCfg *tls.Config, cfg *quic.Config) (quic.EarlySession, error) {
+	sess, err := d.Dialer.DialContext(ctx, network, host, tlsCfg, cfg)
+	err = SafeErrWrapperBuilder{
+		Classifier: ClassifyQUICFailure,
+		Error:      err,
+		Operation:  QUICHandshakeOperation,
+	}.MaybeBuild()
+	if err != nil {
+		return nil, err
+	}
+	return sess, nil
+}