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

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

@@ -0,0 +1,19 @@
+package foo
+
+class B(val name: String)
+
+class A(val a: Int, var b: B) {
+    var copyB: B
+    init {
+        copyB = b
+    }
+}
+
+fun box(): String {
+    val a = A(5, B("OK"))
+    if (a.a != 5) return "a.a != 5, it: ${a.a}"
+    if (a.b.name != "OK") return "a.b.name != 'OK', it: ${a.b.name}"
+    if (a.copyB!!.name != "OK") return "a.b.name != 'OK', it: ${a.copyB!!.name}"
+
+    return "OK"
+}