[JS IR] Fix creating of classes extended from nested one

[JS IR] Extract getClassRef method

 ^KT-44950 fixed

compiler/testData/codegen/box/innerNested/extenderNestedClass.kt

@@ -0,0 +1,9 @@
+object Foo {
+    open class Bar(val bar: String)
+}
+
+class Baz: Foo.Bar("OK")
+
+fun box(): String {
+    return Baz().bar
+}