json: support field &Type (#17655)

vlib/json/json_encode_with_ptr_test.v

@@ -0,0 +1,28 @@
+import json
+
+struct User {
+	name string
+}
+
+struct MyStruct {
+	user   &User //
+	users  map[string]User
+	users2 map[string]&User
+}
+
+fn test_json_encode_with_ptr() {
+	user := User{
+		name: 'foo'
+	}
+	data := MyStruct{
+		user: &user
+		users: {
+			'keyfoo': user
+		}
+		users2: {
+			'keyfoo': &user
+		}
+	}
+
+	assert json.encode(data) == '{"user":{"name":"foo"},"users":{"keyfoo":{"name":"foo"}},"users2":{"keyfoo":{"name":"foo"}}}'
+}