Add more stub generator tests for external dependencies

compiler/testData/ir/irText/stubs/kotlinInnerClass.kt

@@ -0,0 +1,13 @@
+// !DUMP_DEPENDENCIES
+
+// FILE: external.kt
+// EXTERNAL_FILE
+class Outer {
+    inner class Inner {
+        fun foo() {}
+    }
+    fun bar() {}
+}
+
+// FILE: kotlinInnerClass.kt
+fun test(inner: Outer.Inner) = inner.foo()