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/peers/self.go

@@ -0,0 +1,25 @@
+package peers
+
+import (
+	"context"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+// Self returns current User.
+func (m *Manager) Self(ctx context.Context) (User, error) {
+	return m.GetUser(ctx, &tg.InputUserSelf{})
+}
+
+func (m *Manager) selfIsBot() bool {
+	u, ok := m.me.Load()
+	return ok && u.Bot
+}
+
+func (m *Manager) myID() (int64, bool) {
+	u, ok := m.me.Load()
+	if !ok {
+		return 0, false
+	}
+	return u.ID, true
+}