feat: add json and yaml variable constructors

testdata/vars/any2/example.json

@@ -0,0 +1,18 @@
+{
+    "name": "Alice",
+    "age": 30,
+    "children": [
+        {
+            "name": "Bob",
+            "age": 5
+        },
+        {
+            "name": "Charlie",
+            "age": 3
+        },
+        {
+            "name": "Diane",
+            "age": 1
+        }
+    ]
+}