JS/RTTI: support unsafe casts

#KT-2670 fixed

js/js.translator/testData/expression/cast/cases/reifiedToNotNull.kt

@@ -0,0 +1,21 @@
+package foo
+
+// CHECK_NOT_CALLED: test
+
+trait A
+
+class AImpl: A
+
+inline
+fun test<reified T>(x: Any?): T = x as T
+
+fun box(): String {
+    var a: A = AImpl()
+    assertEquals(a, test<A>(a), "a = AImpl()")
+    a = object : A {}
+    assertEquals(a, test<A>(a), "a = object : A{}")
+    failsClassCast("test(null)") { test<A>(null) }
+    failsClassCast("test(object{})") { test<A>(object{}) }
+
+    return "OK"
+}