Support smart cast for nullability in LHS of class literal

#KT-16291 Fixed

compiler/testData/diagnostics/tests/classLiteral/smartCast.kt

@@ -0,0 +1,23 @@
+// KT-16291 Smart cast doesn't work when getting class of instance
+
+import kotlin.reflect.KClass
+
+class Foo {
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other === null || other::class != this::class) return false
+
+        return true
+    }
+}
+
+fun test(f: Foo?): KClass<out Foo>? = if (f != null) f::class else null
+
+fun test2(): KClass<out Foo>? {
+    var f: Foo? = null
+    if (f != null) {
+        run { f = null }
+        return <!EXPRESSION_OF_NULLABLE_TYPE_IN_CLASS_LITERAL_LHS!>f<!>::class
+    }
+    return null
+}