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

lib/twitch-eventsub-ws/ast/lib/templates/field-vector.tmpl

@@ -1,14 +1,14 @@
 {% if field.tag -%}
 static_assert(false && "JSON tag support is not implemented for vectors");
 {%- endif %}
+std::vector<{{field.type_name}}> v{{field.name}};
 const auto *jv{{field.name}} = root.if_contains("{{field.json_name}}");
-if (jv{{field.name}} == nullptr)
-{
-    {% include 'error-missing-field.tmpl' indent content %}
+if (jv{{field.name}} != nullptr && !jv{{field.name}}->is_null()) {
+    auto {{field.name}} = boost::json::try_value_to<std::vector<{{field.type_name}}>>(*jv{{field.name}});
+    if ({{field.name}}.has_error())
+    {
+        {% include 'error-failed-to-deserialize.tmpl' indent content %}
+    } else {
+        v{{field.name}} = std::move({{field.name}}.value());
+    }
 }
-auto {{field.name}} = boost::json::try_value_to<std::vector<{{field.type_name}}>>(*jv{{field.name}});
-if ({{field.name}}.has_error())
-{
-    {% include 'error-failed-to-deserialize.tmpl' indent content %}
-}
-

lib/twitch-eventsub-ws/ast/lib/templates/initializer-vector.tmpl

@@ -1 +1 @@
-.{{field.name}} = std::move({{field.name}}.value()),
+.{{field.name}} = std::move(v{{field.name}}),