menu titles should get their own ID

## Prerequisites

- [ x] I have searched for similar features requests in both open and closed tickets and cannot find a duplicate.
- [ x] The feature is still missing in the latest stable version of Elementor ( Elementor Pro. )

**What problem is your feature request going to solve? Please describe.**
If I want to add custom css to individual menu titles, there's no easy way to reference them because they don't have IDs.

**Describe the solution you'd like**
Give each menu title, the "li" item in css, an id.

**Describe alternatives you've considered**
On a page with no other "li" entries, it's possible to "cheat" by using references like li:nth-child(1).