JS: refactor generation of functions with optional parameters. Fix #KT-7302, #KT-13888

js/js.translator/testData/box/native/callbackOptionalParameter.kt

@@ -0,0 +1,26 @@
+package foo
+
+var global = ""
+
+open class A {
+    open fun foo(x: Int = 23) {
+        global += "A.foo($x);"
+    }
+}
+
+class B : A() {
+    override fun foo(x: Int) {
+        global += "B.foo($x);"
+    }
+}
+
+@native fun bar(a: A)
+
+fun box(): String {
+    bar(A())
+    bar(B())
+
+    if (global != "A.foo(23);A.foo(99);B.foo(23);B.foo(99);") return "fail: $global"
+
+    return "OK"
+}