IR: Allow references to script constructor in module

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

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrScript.kt

@@ -38,4 +38,6 @@ abstract class IrScript :
     abstract var earlierScripts: List<IrScriptSymbol>?
 
     abstract var targetClass: IrClassSymbol?
+
+    abstract var constructor: IrConstructor?
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrScriptImpl.kt

@@ -56,6 +56,7 @@ class IrScriptImpl(
     override var earlierScriptsParameter: IrValueParameter? = null
     override var earlierScripts: List<IrScriptSymbol>? = null
     override var targetClass: IrClassSymbol? = null
+    override var constructor: IrConstructor? = null
 
     @ObsoleteDescriptorBasedAPI
     override val descriptor: ScriptDescriptor

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/irTypes.kt

@@ -14,6 +14,7 @@ import org.jetbrains.kotlin.ir.declarations.IrTypeParametersContainer
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrClassifierSymbol
+import org.jetbrains.kotlin.ir.symbols.IrScriptSymbol
 import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.ir.types.impl.*
 import org.jetbrains.kotlin.ir.util.defaultType
@@ -77,7 +78,12 @@ val IrType.classifierOrNull: IrClassifierSymbol?
     get() = safeAs<IrSimpleType>()?.classifier
 
 val IrType.classOrNull: IrClassSymbol?
-    get() = classifierOrNull as? IrClassSymbol
+    get() =
+        when (val classifier = classifierOrNull)  {
+            is IrClassSymbol -> classifier
+            is IrScriptSymbol -> classifier.owner.targetClass
+            else -> null
+        }
 
 val IrType.classFqName: FqName?
     get() = classOrNull?.owner?.fqNameWhenAvailable