model: Add ChannelPostPolicy.fromInt method

Author: sm-sayedi

lib/api/model/model.dart

@@ -378,6 +378,17 @@ enum ChannelPostPolicy {
   final int? apiValue;
 
   int? toJson() => apiValue;
+
+  /// Get a [ChannelPostPolicy] from a nullable int.
+  ///
+  /// Example:
+  ///   2    -> ChannelPostPolicy.administrators
+  ///   null -> ChannelPostPolicy.unknown
+  static ChannelPostPolicy fromInt(int? value) => _byIntValue[value]!;
+
+  // _$…EnumMap is thanks to `alwaysCreate: true` and `fieldRename: FieldRename.kebab`
+  static final _byIntValue = _$ChannelPostPolicyEnumMap
+    .map((key, value) => MapEntry(value, key));
 }
 
 /// As in `subscriptions` in the initial snapshot.