IR: Allow references to script constructor in module

aso add test checking (somewhat confusing) semantic of
script nested classes.

compiler/testData/codegen/box/script/scriptNestedClassInstance.kt

@@ -0,0 +1,14 @@
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND_FIR: JVM_IR
+// IGNORE_LIGHT_ANALYSIS
+// WITH_RUNTIME
+// FILE: test.kt
+
+fun box(): String =
+    Script.Nested().x
+
+// FILE: script.kts
+
+class Nested {
+    val x = "OK"
+}