JS: create new common directory for all generated tests, migrate several tests there

js/js.translator/testData/box/initialize/rootValInit.kt

@@ -0,0 +1,16 @@
+package foo
+
+class A(val a: Int)
+
+class Empty
+
+val x = 1
+val a = A(2)
+val e = Empty()
+
+fun box(): String {
+    if (x != 1) return "x != 1, it: $x"
+    if (a.a != 2) return "a.a != 2, it: ${a.a}"
+
+    return "OK"
+}