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/zero.tmpl

@@ -0,0 +1,30 @@
+{{ define "zero_derive" }}{{ $s := . }}
+{{- /*gotype: go.mau.fi/mautrix-telegram/pkg/gotd/gen.structDef*/ -}}
+func ({{ $s.Receiver }} *{{ $s.Name }}) Zero() bool {
+    if {{ $s.Receiver }} == nil {
+        return true
+    }
+{{- /*gotype: go.mau.fi/mautrix-telegram/pkg/gotd/gen.fieldDef*/ -}}
+{{- range $f := $s.Fields }}{{- if ne ($f.Name) ($f.ConditionalField) }}
+    if !({{ $s.Receiver }}.{{template "compare_zero" $f}}) {
+        return false
+    }
+{{- end }}{{- end }}
+
+    return true
+}
+{{- end -}}
+
+{{ define "compare_zero" }}
+{{- /*gotype: go.mau.fi/mautrix-telegram/pkg/gotd/gen.fieldDef*/ -}}
+{{- .Name -}}
+{{- if or (.Slice) (.DoubleSlice) -}} == nil
+{{- else if eq (.Type) ("bin.Int128") -}} == bin.Int128{}
+{{- else if eq (.Type) ("bin.Int256") -}} == bin.Int256{}
+{{- else if or (hasPrefix (.Type) ("int")) (hasPrefix (.Type) ("float")) }} == 0
+{{- else if eq (.Type) ("string") -}} == ""
+{{- else if eq (.Type) ("bool") -}} == false
+{{- else if eq (.Type) ("bin.Object") }} == nil
+{{- else if hasSuffix (.Type) ("Class") }} == nil
+{{- else -}}.Zero()
+{{- end -}}{{- end }}