Implement "Override hierarchy" view

idea/testData/hierarchy/overrides/kotlinFunctionInClass/main0.kt

@@ -0,0 +1,27 @@
+open class T {
+    open fun <caret>foo() {
+
+    }
+}
+
+open class X: T() {
+    override fun foo() {
+
+    }
+}
+
+open trait Y: T() {
+    override fun foo() {
+
+    }
+}
+
+open class Z: Y {
+    override fun foo() {
+
+    }
+}
+
+class SS {
+
+}