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/message/peer/convert.go

@@ -0,0 +1,40 @@
+package peer
+
+import (
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+// ToInputUser converts given peer to input user if possible.
+func ToInputUser(user tg.InputPeerClass) (tg.InputUserClass, bool) {
+	switch u := user.(type) {
+	case *tg.InputPeerUser:
+		v := new(tg.InputUser)
+		v.FillFrom(u)
+		return v, true
+	case *tg.InputPeerUserFromMessage:
+		v := new(tg.InputUserFromMessage)
+		v.FillFrom(u)
+		return v, true
+	case *tg.InputPeerSelf:
+		v := new(tg.InputUserSelf)
+		return v, true
+	default:
+		return nil, false
+	}
+}
+
+// ToInputChannel converts given peer to input channel if possible.
+func ToInputChannel(channel tg.InputPeerClass) (tg.InputChannelClass, bool) {
+	switch u := channel.(type) {
+	case *tg.InputPeerChannel:
+		v := new(tg.InputChannel)
+		v.FillFrom(u)
+		return v, true
+	case *tg.InputPeerChannelFromMessage:
+		v := new(tg.InputChannelFromMessage)
+		v.FillFrom(u)
+		return v, true
+	default:
+		return nil, false
+	}
+}