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/combinators.go

@@ -0,0 +1,41 @@
+package gen
+
+func generateSliceHelper(s structDef) bool {
+	return len(s.Fields) > 0 && !s.Vector && s.Method == ""
+}
+
+type simpleField struct {
+	Name        string
+	Type        string
+	Conditional bool
+}
+
+func (s simpleField) match(f fieldDef) bool {
+	return f.Name == s.Name && f.Type == s.Type && f.Conditional == s.Conditional
+}
+
+func collectOnlyFields(fields []fieldDef, matchers ...simpleField) []fieldDef {
+	return filterFieldsTo(fields, nil, func(f fieldDef) bool {
+		for _, matcher := range matchers {
+			if matcher.match(f) {
+				return true
+			}
+		}
+		return false
+	})
+}
+
+func mapCollectableFields(fields []fieldDef) (r []fieldDef) {
+	return collectOnlyFields(fields,
+		simpleField{Name: "ID", Type: "int"},
+		simpleField{Name: "ID", Type: "int64"},
+	)
+}
+
+func sortableFields(fields []fieldDef) (r []fieldDef) {
+	return collectOnlyFields(fields,
+		simpleField{Name: "ID", Type: "int"},
+		simpleField{Name: "ID", Type: "int64"},
+		simpleField{Name: "Date", Type: "int"},
+	)
+}