Remove generated codegen tests, move all testData to box/

A single test file will be generated out of box/ directory

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

@@ -0,0 +1,31 @@
+class Outer {
+    class Nested
+    inner class Inner
+    
+    fun Inner.foo() {
+        Outer()
+        Nested()
+        Inner()
+    }
+    
+    fun Nested.bar() {
+        Outer()
+        Nested()
+        Inner()
+    }
+    
+    fun Outer.baz() {
+        Outer()
+        Nested()
+        Inner()
+    }
+    
+    fun box(): String {
+        Inner().foo()
+        Nested().bar()
+        baz()
+        return "OK"
+    }
+}
+
+fun box() = Outer().box()