JS: test kotlin-test as box tests, support nested, fix mpp

Support tests inside nested classes and companion objects (KT-21850
fixed).
Don't launch multiplatform tests twice (KT-21567 fixed).

js/js.translator/testData/box/kotlin.test/simple.kt

@@ -0,0 +1,16 @@
+// EXPECTED_REACHABLE_NODES: 1173
+import kotlin.test.Test
+
+class Simple {
+    @Test fun foo() {
+        call("foo")
+    }
+}
+
+fun box() = checkLog {
+    suite("Simple") {
+        test("foo") {
+            call("foo")
+        }
+    }
+}