move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/telegram/transfer.go

@@ -0,0 +1,55 @@
+package telegram
+
+import (
+	"context"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+func (c *Client) exportAuth(ctx context.Context, dcID int) (*tg.AuthExportedAuthorization, error) {
+	export, err := c.tg.AuthExportAuthorization(ctx, dcID)
+	if err != nil {
+		return nil, errors.Wrapf(err, "export auth to %d", dcID)
+	}
+
+	return export, nil
+}
+
+// AuthTransferHandler is a function that is called during authorization transfer.
+//
+// The fn callback should be serialized by user id via external locking.
+// You can call [Client.Self] to acquire current user id.
+//
+// The fn callback must return fn error if any.
+type AuthTransferHandler func(ctx context.Context, client *Client, fn func(context.Context) error) error
+
+func noopOnTransfer(ctx context.Context, _ *Client, fn func(context.Context) error) error {
+	return fn(ctx)
+}
+
+// transfer exports current authorization and imports it to another DC.
+// See https://core.telegram.org/api/datacenter#authorization-transfer.
+func (c *Client) transfer(ctx context.Context, to *tg.Client, dc int) (tg.AuthAuthorizationClass, error) {
+	var out tg.AuthAuthorizationClass
+	if err := c.onTransfer(ctx, c, func(ctx context.Context) error {
+		auth, err := c.exportAuth(ctx, dc)
+		if err != nil {
+			return errors.Wrapf(err, "export to %d", dc)
+		}
+
+		req := &tg.AuthImportAuthorizationRequest{}
+		req.FillFrom(auth)
+		r, err := to.AuthImportAuthorization(ctx, req)
+		if err != nil {
+			return errors.Wrapf(err, "import from %d", dc)
+		}
+
+		out = r
+		return nil
+	}); err != nil {
+		return nil, errors.Wrap(err, "onTransfer")
+	}
+	return out, nil
+}