JS: move expressions test to box tests

js/js.translator/testData/box/expression/invoke/extensionInvoke.kt

@@ -0,0 +1,16 @@
+package foo
+
+class A(val f: (B.() -> Int)?)
+
+class B(val x: Int)
+
+fun test(g: (B.() -> Int)?): Int? {
+    val a = A(g)
+    val b = B(2)
+    return a.f?.invoke(b)
+}
+
+fun box(): String {
+    assertEquals(5, test { x + 3 })
+    return "OK"
+}