JS: move expressions test to box tests

js/js.translator/testData/box/expression/misc/KT-1865.kt

@@ -0,0 +1,15 @@
+package foo
+
+open class A {
+    open fun foo(a: Int = 1) = a
+}
+
+class B : A() {
+    override fun foo(a: Int) = a + 1
+}
+
+fun box(): String {
+    val result = B().foo()
+    if (result != 2) return "fail: $result"
+    return "OK"
+}