nav-menu tabs turn into a select when there are too many menus

[Sverigedemokraterna IT]

The menu editor tab bar isn't a very effective way to select menus if you have, say, 10 or 20 menus or so. This patch changes the tab bar to a select + button in a form.

Things to note:

• The define (5) is arbitrary and can perhaps be placed elsewhere.
• Using a GET was the smartest way of selecting another menu, while at the same time remaining accessibility-friendly.
• Using the GET causes the button to end up on the address bar also. This could have been avoided if the submit button could have the button text and the value separately (perfect value is "edit"), but that's HTML for you.
• I'm unsure of correct CSS styling.

[Sverigedemokraterna IT]

Changes tab bar to a select if there are too many menus

[johnbillion]

+1 for the idea. We definitely need a better way of presenting menus when there are a large number of them.

[nacin]

I think we should remove the tabs all together. User testing will likely validate that the tabs greatly confuse users into thinking they are the menu itself.

[lessbloat]

Replying to nacin:

I think we should remove the tabs all together. User testing will likely validate that the tabs greatly confuse users into thinking they are the menu itself.

No sign of trouble with the ​first two user tests. But I agree, this could very likely be designed better.

[SergeyBiryukov]

Related: #23119

[lessbloat]

We removed tabs completely in #23119.