Show all non-core submenu entries after a divider

[zodiac1978]

The admin UI is not very customizable. We can't move menu entries around or hide specific ones in the UI itself (only via code).

The benefit of this is, that training/support/tutorials always know where to send the user.

But if there are many plugins installed the admin UI can still get a mess. As a first little step in the direction of make the UI more tidy I would like to suggest showing the core items of a submenu first and then after a divider show the added submenu items in alphabetically order.

This is exactly what this plugin does:
​https://wordpress.org/plugins/sortacular/
​https://github.com/DLXPlugins/sortacular

Unfortunately this will get closed soon (on 1st of October):
​https://dlxplugins.com/announcements/dlxplugins-is-closing/

Adding this to core would make the UI more consistent. People do not need to look for the core items in a long list of e.g. plugin settings.