Support smart cast for nullability in LHS of class literal

#KT-16291 Fixed

compiler/testData/codegen/box/classLiteral/bound/smartCast.kt

@@ -0,0 +1,11 @@
+// KT-16291 Smart cast doesn't work when getting class of instance
+
+class Foo(val s: String) {
+    override fun equals(other: Any?): Boolean {
+        return other != null && other::class == this::class && s == (other as Foo).s
+    }
+}
+
+fun box(): String {
+    return if (Foo("a") == Foo("a")) "OK" else "Fail"
+}