Describe the new feature:
In #32572, we still need to use unsafe code to create Funtion. The FunctionBinging doesn't provide a safe way to create one. And considering many dom types don't really want Function. Instead, they just want the *mut JSObject from *mut JSFunction:

• https://github.com/servo/servo/blob/main/components/script/dom/bindings/interface.rs#L341
• https://github.com/servo/servo/blob/main/components/script/dom/promise.rs

We should propose a safe wrapper function(s) for JS_NewFunction and JS_GetFunctionObject. Here are the method I think we could add:

• Function::new_native: Create a Rc<Function> using JS_NewFunction, JS_GetFunctionObject and Function::new
• Function::new_raw_obj: Create a *mut JSObject(or handle?) using JS_NewFunction and JS_GetFunctionObject