Gin theme: Improve compatibility support

Problem/Motivation

Recent changes to the module and maybe to the Gin Admin Theme as well, seem to have broken certain features of the module, in particular the integration with the Admin Toolbar JS dropdown features, see:

#3539006: Dropdown no longer work in Gin:

The 3.5 version Admin toolbar works fine with Gin, but after upgrading to 3.6.x the dropdowns stop working. Unfortunately, there are no obvious console errors to provide for troubleshooting purposes.

or the 'Edit' link added by local tasks, see: #3555727: Gin support: Link edit has disappeared:

After update module, the edit link has disappeared. Why ?

Updated from/to:

• Admin Toolbar (3.5.3 to 3.6.2)
• Drupal (11.1.7 to 11.2.5)
• Gin Toolbar (2.0.0 to 3.0.2)
• Gin (4.0.6 to 5.0.5)

It looks like the upgrades of the Gin Theme were quite significant: Major version upgrades

• Gin Toolbar (2.0.0 to 3.0.2)
• Gin (4.0.6 to 5.0.5)

So we should most likely look into the most recent changes on the Gin Theme side, to see how the module could improve its integration, to maybe at least try to retain the same features as previously.

Some work has already been done on this, in a different ticket with some code implemented, see:
#3304810-59: Toggle away Admin Toolbar completely

Okay, I've added CSS + icons. I've also tested and fixed Gin, with its four toolbar styles.

Moved the .toolbar-expand-floating-button into body, because Gin hides #toolbar-administration in some situations.

I haven't checked smaller viewports / mobile yet.

I think we should not use hide(), show() and toggle() as function names in the JS file, as all three are jQuery functions, which is confusing. My naming is certainly not perfect yet either.

I am not sure about the settings.initial_toolbar_padding_top / settings.initial_toolbar_margin_left. What is the purpose of these settings? I am not a big fan of manipulating styles in JS. If possible, we should set classes instead and put the required CSS in admin_toolbar_toggle.css.

EDIT: Another note - due to the old CSS float technique, we cannot easily add the Hide Trigger button as the last element (visually). There are several outdated frontend techniques used by the admin toolbar. Gin has already fixed all of them, maybe it is a good idea to apply these styles some day.

In particular: try to get back all the work that was done for the Gin Theme support in merge request:
https://git.drupalcode.org/project/admin_toolbar/-/merge_requests/70

Review the issue and see if there could be any other related piece of code we could use for the integration with the Gin Theme.

Feel free to add more problems and/or screenshots illustrating compatibility issues with the Gin Theme.

Steps to reproduce

Install the Gin Admin Theme with the Admin Toolbar module.
Enable the Gin Theme Toolbar module as well and test the integration by changing the settings for the toolbar in the Git theme settings.
@TODO: Provide more detailed testing steps for the settings that really reproduce visible/testable issues.

Proposed resolution

Try to exploit any work that was done previous in:
https://git.drupalcode.org/project/admin_toolbar/-/merge_requests/70

and try to fix as much as possible the integration with the Gin Theme, based on reported issues.

Admin Toolbar Search:

Provide support for the Admin Toolbar Search with the Gin Theme, in particular with the following features:
#3564229-3: Admin Toolbar Search: Refactor admin_toolbar_search.js

• Provide different ways to load the Search field on the page (not only in the toolbar) ==> Support also Navigation, Gin, etc...
• Allow the menu links selector to be configurable to pick up links from any menu or markup on the page, for example to support core Navigation and pick up its links instead.

Remaining tasks

User interface changes

API changes

Data model changes