[2.x] Rewrite navigation internals

[emmadesilva]

TLDR: This breaks... everything. The entire Navigation API is essentially rewritten. The easiest way to upgrade is going to be reimplementing existing code from scratch.

New attempt at fixing #1508 after closing #1538. It targets HydePHP v2 #1565

With this, NavigationMenu classes are no longer responsible for generating the menus, instead the API is changed so that they are just data containers. This better follows SOLID principles, and changes the point where we generate the menus in a way that's more controllable.

This rewrites the navigation internals in a few breaking ways. (Note that this list may be incomplete/outdated, the final version will be present in the release notes)

1. Breaking: Change configuration option docs.sidebar_order to docs.sidebar.order
2. Breaking: Change configuration option docs.table_of_contents to docs.sidebar.table_of_contents
3. Breaking: The NavItem::fromRoute() method is now NavItem::forRoute()
4. Breaking: The docs.sidebar.footer no longer supports true as a value
5. Breaking: Rename class NavigationMenu to MainNavigationMenu
6. Breaking: Remove class MainNavigationMenu (essentially replaced/rewritten to the new NavigationMenu class)
7. Breaking: Remove class BaseNavigationMenu
8. Breaking: Remove class DropdownNavItem
9. Breaking: Make BaseNavigationMenu::$items protected
10. Breaking: NavItem::$destination is now a Route instead of string (This is necessary in order to defer route resolving to compile time)
11. Breaking: Remove method DocumentationSidebar::getGroups
12. Breaking: Remove method DocumentationSidebar::getItemsInGroup
13. Breaking: Remove method DocumentationSidebar::makeGroupTitle
14. Deprecate class BaseNavigationMenu
15. Deprecate class MainNavigationMenu
16. Deprecate class DocumentationSidebar
17. Deprecate class DropdownNavItem
18. Deprecate method DocumentationSidebar::makeGroupTitle()
19. Merges DropdownNavItem features into main NavItem class

Changes:

• Adds a new NavigationMenu class
• Adds a new NavigationManager class
• Adds a NavigationServiceProvider to register the manager as a singleton and register a booted callback to the kernel to generate the navigation
• Adds a new child array to NavItem classes to manage dropdowns
• Add a NavItem::dropdown() facade helper
• Make navigation item duplicate filtering case insensitive (could have side effects)
• Merges [2.x] Update NavItem class to support deferring route resolves #1539
• Merges [2.x] Change default DocumentationPage group to be null instead of 'other' #1572
• Merges [2.x] Remove duplicate navigation item filtering #1573
• Merges [2.x] Change NavItem class API to be fluent instead of readonly #1574
• Merges [2.x] Improved navigation group label generation #1576
• Merges [2.x] Simplify dropdown data handling #1577
• Merges [2.x] Refactor navigation menu generators #1578
• Merges [2.x] Merge menu generator actions into single class #1579
• Merges [2.x] Split out base navigation menu class from main menu class #1580
• Merges [2.x] Refactor navigation menu container bindings #1581
• Merges [2.x] Breaking: Change configuration option docs.sidebar_order to docs.sidebar.order #1583
• Merges [2.x] Breaking: Change configuration option docs.table_of_contents to docs.sidebar.table_of_contents #1584
• Merges [2.x] Support setting sidebar labels and visibility in docs config #1586
• Merges [2.x] Refactor sidebar data handling #1587
• Merges [2.x] Massively simplify sidebar footer text handling #1594
• Merges [2.x] Always place navigation menu items in dropdowns when set in front matter #1597
• Merges [2.x] Create positioning priority constants in the navigation menu class #1598
• Merges [2.x] Refactor NavItem class #1599
• Merges [2.x] Rename NavItem fields to normalize its API #1600
• Merges [2.x] Extract back NavItem class for dropdowns #1601
• Merges [2.x] Create HTML tests for the navigation layouts  #1605
• Merges [2.x] Clean up navigation view markup #1606
• Merges [2.x] Normalize navigation HTML ID naming #1622
• Merges [2.x] Expand abbreviated navigation item class names #1625
• Merges [2.x] Restructure navigation item class design to use composition over inheritance #1626
• Merges [2.x] Simplify navigation item group state handling to be deterministic #1632
• Merges [2.x] Create new navigation destination class to replace external routes #1636
• Merges [2.x] Simplify the navigation items class #1637
• Merges [2.x] Create better fallbacks when not supplying a navigation item label #1638
• Merges [2.x] Remove the group property from the navigation item class #1639
• Merges [2.x] Remove the NavigationElement contract #1640
• Merges [2.x] Simplify and normalize public navigation APIs #1642

Since the navigation menu is now essentially cached in the kernel, instead of being created each time the component is rendered, the kernel must be cleared during some tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.97%. Comparing base (c42d912) to head (d0bc2d4).

Additional details and impacted files

@@             Coverage Diff              @@
##             2.x-dev    #1568     +/-   ##
============================================
  Coverage      99.97%   99.97%             
+ Complexity      3504     1775   -1729     
============================================
  Files            364      184    -180     
  Lines           9474     4791   -4683     
============================================
- Hits            9472     4790   -4682     
+ Misses             2        1      -1     

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[emmadesilva]

Should be in its own test