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/mtproto/session.go

@@ -0,0 +1,37 @@
+package mtproto
+
+import "go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+
+// Session represents connection state.
+type Session struct {
+	ID   int64
+	Key  crypto.AuthKey
+	Salt int64
+}
+
+// Session returns current connection session info.
+func (c *Conn) session() Session {
+	c.updateSalt()
+
+	c.sessionMux.RLock()
+	defer c.sessionMux.RUnlock()
+	return Session{
+		Key:  c.authKey,
+		Salt: c.salt,
+		ID:   c.sessionID,
+	}
+}
+
+// newSessionID sets session id to random value.
+func (c *Conn) newSessionID() error {
+	id, err := crypto.RandInt64(c.rand)
+	if err != nil {
+		return err
+	}
+
+	c.sessionMux.Lock()
+	defer c.sessionMux.Unlock()
+	c.sessionID = id
+
+	return nil
+}