show icon of class initializer

#KT-11775 Fixed

idea/testData/structureView/fileStructure/LocalElements.after

@@ -2,4 +2,6 @@
  -foo(): Unit
   bar(): Unit
   -X
+   -<class initializer>
+    quux(): Unit
    xyzzy(): Unit

idea/testData/structureView/fileStructure/LocalElements.kt

@@ -2,6 +2,11 @@ fun foo() {
     fun bar() { }
 
     class X {
+        init {
+            fun quux() {
+            }
+        }
+
         fun xyzzy() {
         }
     }