[5.x]: Entry type groups missing from actions menu

[gglnx]

What happened?

Description

Currently, all entry types are listed without the group headings in a block's actions menu (to add a new block above).

Steps to reproduce

1. Create a Matrix field with two entry type groups.
2. Edit an entry, create a Matrix block, and then click on its actions menu.

Expected behavior

All group headings are also visible in the actions menu, like in the create discloure menu:

Actual behavior

All entry types are listed ungrouped:

Craft CMS version

5.8.5

PHP version

No response

Operating system and version

No response

Database type and version

No response

Image driver and version

No response

Installed plugins and versions

[superflausch]

Yes, this gets messy once there are many block types. One idea could be to nest the entry types into submenus for each group — similar to what’s planned with the button groups in this PR.

For illustration, here’s an example of a submenu from Notion:

[superflausch]

This could also help with the “Delete” action, which often gets pushed way down in the menu and is cumbersome to reach quickly.

[davidhellmann]

I like it and therefore don't dare ask. Could there still be an option to specify whether to use a single dropdown or a group dropdown? I'm asking because some of my authors like the "OLD" approach more. And of course, I still want to have the groups, but I just want to be able to choose which view I want.