all: change optional to option (#16914)

vlib/json/json_decode_with_option_arg_test.v

@@ -0,0 +1,19 @@
+import json
+import os
+
+struct DbConfig {}
+
+fn test_json_decode_with_option_arg() {
+	if ret := print_info() {
+		println(ret)
+	} else {
+		println(err)
+	}
+	assert true
+}
+
+fn print_info() !string {
+	dbconf := json.decode(DbConfig, os.read_file('dbconf.json')!)!
+	println(dbconf)
+	return '${dbconf}'
+}