firewall: add custom ArrayField type to contain rules and add serializer to internal firewall format.

Example usage:

```
$mdlFilter = new OPNsense\Firewall\Filter();

foreach ($mdlFilter->rules->rule->iterateItems() as $key => $rule) {
    print_r($rule->serialize());
}
```

for https://github.com/opnsense/plugins/issues/1720

net/firewall/src/opnsense/mvc/app/models/OPNsense/Firewall/FieldTypes/FilterRuleField.php

@@ -0,0 +1,103 @@
+<?php
+
+/**
+ *    Copyright (C) 2020 Deciso B.V.
+ *
+ *    All rights reserved.
+ *
+ *    Redistribution and use in source and binary forms, with or without
+ *    modification, are permitted provided that the following conditions are met:
+ *
+ *    1. Redistributions of source code must retain the above copyright notice,
+ *       this list of conditions and the following disclaimer.
+ *
+ *    2. Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *
+ *    THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ *    INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ *    AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ *    AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
+ *    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ *    SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ *    INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ *    CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ *    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ *    POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+namespace OPNsense\Firewall\FieldTypes;
+
+use OPNsense\Base\FieldTypes\ArrayField;
+use OPNsense\Base\FieldTypes\ContainerField;
+
+/**
+ * Class FilterRuleContainerField
+ * @package OPNsense\Firewall\FieldTypes
+ */
+class FilterRuleContainerField extends ContainerField
+{
+    /**
+     * map rules
+     * @return array
+     */
+    public function serialize()
+    {
+        $result = array();
+        $map_manual = ['source_net', 'source_not', 'source_port', 'destination_net', 'destination_not',
+            'destination_port', 'enabled', 'description', 'sequence', 'action'];
+        // 1-on-1 map (with type conversion if needed)
+        foreach ($this->iterateItems() as $key => $node) {
+            if (!in_array($key, $map_manual)) {
+                if (is_a($node, "OPNsense\\Base\\FieldTypes\\BooleanField")) {
+                    $result[$key] = !empty((string)$node);
+                } else {
+                    $result[$key] = (string)$node;
+                }
+            }
+        }
+        // source / destination mapping
+        $result['source'] = array();
+        if (!empty((string)$this->source_net)) {
+            $result['source']['network'] = (string)$this->source_net;
+            $result['source']['not'] = !empty((string)$this->source_not);
+            if (!empty((string)$this->source_port)) {
+                $result['source']['port'] = (string)$this->source_port;
+            }
+        }
+        $result['destination'] = array();
+        if (!empty((string)$this->destination_net)) {
+            $result['destination']['network'] = (string)$this->destination_net;
+            $result['destination']['not'] = !empty((string)$this->destination_not);
+            if (!empty((string)$this->source_port)) {
+                $result['destination']['port'] = (string)$this->destination_port;
+            }
+        }
+        // swap enabled
+        $result['disabled'] = empty((string)$this->enabled);
+        //
+        $result['descr'] = (string)$this->description;
+        $result['type'] = (string)$this->action;
+        return $result;
+    }
+}
+
+/**
+ * Class FilterRuleField
+ * @package OPNsense\Firewall\FieldTypes
+ */
+class FilterRuleField extends ArrayField
+{
+    /**
+     * @inheritDoc
+     */
+    public function newContainerField($ref, $tagname)
+    {
+        $container_node = new FilterRuleContainerField($ref, $tagname);
+        $parentmodel = $this->getParentModel();
+        $container_node->setParentModel($parentmodel);
+        return $container_node;
+    }
+}

net/firewall/src/opnsense/mvc/app/models/OPNsense/Firewall/Filter.xml

@@ -5,14 +5,14 @@
     </description>
     <items>
         <rules>
-            <rule type="ArrayField">
+            <rule type=".\FilterRuleField">
                 <enabled type="BooleanField">
                     <default>1</default>
                     <Required>Y</Required>
                 </enabled>
                 <sequence type="IntegerField">
                     <MinimumValue>1</MinimumValue>
-                    <MaximumValue>1000000</MaximumValue>
+                    <MaximumValue>99999</MaximumValue>
                     <ValidationMessage>provide a valid sequence for sorting</ValidationMessage>
                     <Required>Y</Required>
                     <default>1</default>