Consider changing the menu-link Add form to be consistent with the Edit form.

Problem/Motivation

This idea came up as a follow-up issue for this 📌 Improve menu parent link selection Needs work issue.
Currently, the Add form only shows elements of the selected menu as possible parent links. That was a good idea before this 📌 Improve menu parent link selection Needs work issue, but it is worth reconsidering once this 📌 Improve menu parent link selection Needs work issue is fixed. I think it would simplify the code and make the two forms more consistent if we simply set a default value for the Menu select list.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet