Support Deeper Navigation Levels

This is a nice to have, so setting priority as Minor.

Adding the designs for the 4th level.

These styles currently added in drawer/menus tickets. We need to test how they work after recent iterations

I tested the current implementation. I have limited knowledge of the current state of the designs, but the implementation seems consistent:
I am uploading 3 screenshots from the current state:
- Menu level 4 not active without hover
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- Menu level 4 not active with hover
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-Menu level 4 active with hover
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Nothing against this, I guess the question I would ask is, is a better solution ultimately to flatten the admin hierarchy a bit so it's less deep.

Now, yes I'm aware that's more of a longer term view and doesn't help existing sites which need this now, but since this is already a low priority issue, figured I'd bring this up.

Navigation overall supports more menu that are active in the overall project than just Administration as our first focus. Many other menu's do often have 4-6 layers too.
Yes, as Navigation should be able to handle any menu that has greater depth!

Redirecting the depth of what is in 'all the modules' that add into this one menu and their organizing is the extending goal. This would then need followup against every other (core component) that is providing the link/links.

@AaronMcHale of course the ultimate goal should be to improve the IA, but that is out of scope for the Navigation. That should happen independently on 🌱 Restructure the admin interface Information Architecture Active .

Just wanted to check if we are considering how to navigate to the page if it has children. Ie, to resolve 🐛 Second level menu items can't be reached if they have children Active type of problem where if something has children you can only navigate to the lowest child then navigate back up via breadcrumbs.

Enabling level 3 menus (grandchild items) would be extremely useful to the Navigation Extra Tools module.

I'm working on replicating functionality from the Admin Toolbar Extra Tools ✨ Add bundle derivatives like admin_toolbar_tools Active module to place entity items as sub-items in the Navigation menus.

For example, the level 1 Content Types menu gets expanded to show a list of content types as level 2 items, which would expand to options like "manage fields" and "manage display" as level 3 items, if those were available.

I think the level 2 items are still helpful, but we're dependent on this issue to provide the level 3 items.

Updating the issue summary with final designs for a fourth level. Note that we have "Overview" links here. This is meant to link to the parent page, since the click on that parent expands/collapses the child menu, and does not click through. The "Overview" link funcionality is the subject of 🐛 Second level menu items can't be reached if they have children Active .

Those look nice!