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/query/channels/participants/specialize.go

@@ -0,0 +1,62 @@
+package participants
+
+import (
+	"go.mau.fi/mautrix-telegram/pkg/gotd/telegram/query/photos"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+// UserPhotos returns new user photo query builder for participant.
+func (e Elem) UserPhotos(raw *tg.Client) (*photos.GetUserPhotosQueryBuilder, bool) {
+	user, ok := e.User()
+	if !ok {
+		return nil, false
+	}
+	return photos.NewQueryBuilder(raw).GetUserPhotos(user.AsInput()), true
+}
+
+// User tries to get participant user object.
+func (e Elem) User() (*tg.User, bool) {
+	switch part := e.Participant.(type) {
+	case interface{ GetUserID() int64 }:
+		return e.Entities.User(part.GetUserID())
+	case interface{ GetPeer() tg.PeerClass }:
+		user, ok := part.GetPeer().(*tg.PeerUser)
+		if !ok {
+			return nil, false
+		}
+
+		return e.Entities.User(user.GetUserID())
+	default:
+		return nil, false
+	}
+}
+
+// Creator returns participant user object and meta info if participant is a creator of channel.
+func (e Elem) Creator() (*tg.User, *tg.ChannelParticipantCreator, bool) {
+	part, ok := e.Participant.(*tg.ChannelParticipantCreator)
+	if !ok {
+		return nil, nil, false
+	}
+
+	user, ok := e.User()
+	if !ok {
+		return nil, nil, false
+	}
+
+	return user, part, true
+}
+
+// Admin returns participant user object and meta info if participant is admin of channel.
+func (e Elem) Admin() (*tg.User, *tg.ChannelParticipantAdmin, bool) {
+	part, ok := e.Participant.(*tg.ChannelParticipantAdmin)
+	if !ok {
+		return nil, nil, false
+	}
+
+	user, ok := e.User()
+	if !ok {
+		return nil, nil, false
+	}
+
+	return user, part, true
+}