[JS IR] Add tests for KT-41964 and KT-44981

js/js.translator/testData/box/jsCode/kt44981.kt

@@ -0,0 +1,12 @@
+// EXPECTED_REACHABLE_NODES: 1267
+
+const val x = '2'
+const val y = '+'
+const val z = '3'
+
+fun box(): String {
+    if (js(x.toString() + z) !== 23) return "Fail 1"
+    if (js(x.toString() + y + z) !== 5) return "Fail 2"
+
+    return "OK"
+}