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/tgtest/vector.go

@@ -0,0 +1,26 @@
+package tgtest
+
+import (
+	"fmt"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+// genericVector is a simple helper to encode a vector of TL objects.
+type genericVector struct {
+	Elems []bin.Encoder
+}
+
+// Encode implements bin.Encoder.
+func (vec *genericVector) Encode(b *bin.Buffer) error {
+	b.PutVectorHeader(len(vec.Elems))
+	for idx, v := range vec.Elems {
+		if v == nil {
+			return fmt.Errorf("unable to encode Vector<%T>: field Elems element with index %d is nil", v, idx)
+		}
+		if err := v.Encode(b); err != nil {
+			return fmt.Errorf("unable to encode Vector<%T>: field Elems element with index %d: %w", v, idx, err)
+		}
+	}
+	return nil
+}