JS backend: move patternMatching tests to expression/when

js/js.translator/testData/expression/when/cases/whenWithOnlyElse.kt

@@ -0,0 +1,9 @@
+package foo
+
+fun box(): Boolean {
+    var a = 0
+    when (a) {
+        else -> a = 2
+    }
+    return a == 2
+}