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

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

@@ -0,0 +1,24 @@
+package foo
+
+data class A(private val x: Int) {
+    val y: Int
+        get() = x
+}
+
+fun box(): String {
+    val a = A(23)
+
+    assertEquals("A(x=23)", a.toString())
+    assertEquals(23, a.copy().y)
+    assertEquals(42, a.copy(42).y)
+
+    assertEquals(A(23), A(23))
+    assertNotEquals(A(42), A(23))
+
+    val map = mapOf(A(23) to "*", A(42) to "@")
+    assertEquals("*", map[A(23)])
+    assertEquals("@", map[A(42)])
+    assertEquals(null, map[A(93)])
+
+    return "OK"
+}