Inheritors in smart completion work for the classes in the same file too

idea/testData/completion/smartMultiFile/InheritorInTheSameFile/InheritorInTheSameFile.kt

@@ -0,0 +1,11 @@
+open class A : T
+
+fun foo(): T {
+    return <caret>
+}
+
+class B : T
+
+// EXIST: A
+// EXIST: B
+// EXIST: C