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/gen/_template/set_flags.tmpl

@@ -0,0 +1,15 @@
+{{- /*gotype: go.mau.fi/mautrix-telegram/pkg/gotd/gen.structDef*/ -}}
+{{ define "set_flags" }}{{ $s := . }}
+{{- if hasFlags $s }}
+// SetFlags sets flags for non-zero fields.
+func ({{ $s.Receiver }} *{{ $s.Name }}) SetFlags() {
+{{- range $f := $s.Fields }}
+    {{- if $f.Conditional }}
+        if !({{ $s.Receiver }}.{{template "compare_zero" $f}}) {
+        {{ $s.Receiver }}.{{ $f.ConditionalField }}.Set({{ $f.ConditionalIndex }})
+        }
+    {{- end }}
+{{- end }}
+}
+{{- end }}
+{{ end }}