generate bytecode for script

It is just prototype

* does not make top level symbols visible as class members yet
* does not take parameters
* Script class name is hardcoded now

compiler/testData/codegen/script/topLevelFunction.ktscript

@@ -0,0 +1,11 @@
+// expected: 3628800
+
+fun factorial(n: Int): Int {
+    var product = 1
+    for (i in 1..n) {
+        product *= i
+    }
+    return product
+}
+
+factorial(10)