Add aggregateWindow() function to Query Builder

Signed-off-by: davidarendsen <davidarendsen@hey.com>

src/Type/FnType.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace Arendsen\FluxQueryBuilder\Type;
+
+class FnType implements TypeInterface
+{
+    public function __construct(string $value)
+    {
+        $this->value = $value;
+    }
+
+    public function __toString(): string
+    {
+        return $this->value;
+    }
+}