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

js/js.translator/testData/box/extensionFunction/extensionFunctionCalledFromExtensionFunction.kt

@@ -0,0 +1,12 @@
+package foo
+
+class A() {
+
+}
+
+fun A.one() = 1
+fun A.two() = one() + one()
+
+fun box(): String {
+    return if (A().two() == 2) "OK" else "fail"
+}