feat(eventsub): Add support for channel.moderate Warn (#5932)

* fix(eventsub): Be less strict with strings & vectors

String foo from `{"foo":null}` is now accepted, and returns an empty string
std::vector<String> foo from `{"foo":null}` is now accepted, and returns an empty array

src/providers/twitch/eventsub/MessageBuilder.cpp

@@ -78,4 +78,66 @@ MessagePtr makeUnvipMessage(
     return builder.release();
 }
 
+MessagePtr makeWarnMessage(
+    TwitchChannel *channel, const QDateTime &time,
+    const lib::payload::channel_moderate::v2::Event &event,
+    const lib::payload::channel_moderate::v2::Warn &action)
+{
+    MessageBuilder builder;
+
+    QString text;
+
+    builder.emplace<TimestampElement>();
+    builder->flags.set(MessageFlag::System);
+    builder->flags.set(MessageFlag::Timeout);
+    builder->loginName = event.moderatorUserLogin.qt();
+
+    builder.emplace<MentionElement>(
+        event.moderatorUserName.qt(), event.moderatorUserLogin.qt(),
+        MessageColor::System,
+        channel->getUserColor(event.moderatorUserLogin.qt()));
+    text.append(event.moderatorUserLogin.qt() + " ");
+
+    builder.emplaceSystemTextAndUpdate("has warned", text);
+
+    builder
+        .emplace<MentionElement>(action.userName.qt(), action.userLogin.qt(),
+                                 MessageColor::System,
+                                 channel->getUserColor(action.userLogin.qt()))
+        ->setTrailingSpace(false);
+    text.append(action.userLogin.qt());
+
+    QStringList reasons;
+
+    if (!action.reason.qt().isEmpty())
+    {
+        reasons.append(action.reason.qt());
+    }
+
+    for (const auto &rule : action.chatRulesCited)
+    {
+        if (!rule.qt().isEmpty())
+        {
+            reasons.append(rule.qt());
+        }
+    }
+
+    if (reasons.isEmpty())
+    {
+        builder.emplaceSystemTextAndUpdate(".", text);
+    }
+    else
+    {
+        builder.emplaceSystemTextAndUpdate(":", text);
+        builder.emplaceSystemTextAndUpdate(reasons.join(", "), text);
+    }
+
+    builder.message().messageText = text;
+    builder.message().searchText = text;
+
+    builder.message().serverReceivedTime = time;
+
+    return builder.release();
+}
+
 }  // namespace chatterino::eventsub