Scripting: add the missing app.preferences.saveToDisk() so imported scripts like Duik get past startup (#1263)

crates/script/src/prelude.js

@@ -1978,6 +1978,7 @@ var app = {
     savePrefAsBool: function () {},
     savePrefAsFloat: function () {},
     reload: function () {},
+    saveToDisk: function () {},
   },
   newProject: function () { __call("file.newProject", {}); return new Project(); },
   open: function (file) {

crates/script/src/tests_callable.rs

@@ -94,3 +94,10 @@ fn calling_without_a_name_is_a_script_error() {
     let o = ok(&mut s, "var c = app.project.items.addComp('N', 100, 100, 1, 1, 25); var l = c.layers.addNull(); l.name = 'Ctl'; l");
     assert_eq!(o.result, json!({ "type": "[object AVLayer]", "name": "Ctl" }));
 }
+
+#[test]
+fn app_preferences_save_to_disk_is_callable() {
+    let mut s = session();
+    let o = ok(&mut s, "app.preferences.saveToDisk(); app.preferences.reload(); [typeof app.preferences.saveToDisk, app.preferences.getPrefAsLong('a', 'b')]");
+    assert_eq!(o.result, json!(["function", 0]));
+}