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

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

@@ -0,0 +1,14 @@
+package foo
+
+fun f() {}
+fun selector() = true
+
+val y = if (selector()) 23 else throw Exception()
+val x = if (selector()) { f(); y + 1 } else 999
+val z = if (selector()) { f(); x + 1 } else 999
+
+fun box(): String {
+    if (x != 24) return "fail1: $x"
+    if (z != 25) return "fail2: $z"
+    return "OK"
+}