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

js/js.translator/testData/box/dataClass/copy.kt

@@ -0,0 +1,11 @@
+package foo
+
+data class Dat(val start: String, val middle: String, val end: String)
+
+fun box(): String {
+    val d1 = Dat("OO", "-", "PS")
+    val d2: Dat = d1.copy(end = "K", middle = "+")
+    val d3: Dat = d2.copy(start = "O", middle = "-")
+    val (p1, p, p2) = d3
+    return p1 + p2
+}