Introduction of CastedClassReceiver and its handling in codegen #KT-6744 Fixed

ClassReceiver converted to Kotlin
Also #KT-7617 Fixed

compiler/testData/codegen/box/smartCasts/implicitReceiver.kt

@@ -0,0 +1,13 @@
+open class A {
+    class B : A() {
+        val a = "FAIL"
+    }
+
+    fun foo(): String {
+        if (this is B) return a
+        return "OK"
+    }
+}
+
+
+fun box(): String = A().foo()