Global Search: Split search results into tabs by category

Requisites

1. A site with courses, users, activities (bigger is better although you also can try this in a small one as far as there is some word like "testing" or so present often.
2. Having the site indexed for global search.

Description

There are three new  search results display options added to the search admin interface (/admin/category.php?category=searchplugins):

1. Display results in separate categories (yes/no)
2. Default search category (Select list)
3. Hide All results category (yes/no)
   These will be shown in the search results page when configured.

Testing admin UI

1. Verify that the 3 settings above are shown.
2. Verify that the "Search areas" page (/admin/searchareas.php) now displays a list of categories for each area.

Search testing

Testing should cover all combinations of admin settings.

1. If "Display results in separate categories" is set to No: global search results should remain the same as it is now.
2. "Display results in separate categories" = yes, Default search category = All, "Hide All results category" = no: global search results should be spit by 5 tabs (All, Course content, Courses, Users, Other). User can switch between tabs and see only relevant to selected tab (category) list of items. Search area filter on each tab should display only areas associated to the selected category. Search area filter should reset if you switch between tabs. When a user search initially,  All tab should be displayed.
3. "Display results in separate categories" = yes, Default search category = All, "Hide All results category" = yes: global search results should be spit by 4 tabs (Course content, Courses, Users, Other).  When a user search initially, Course content tab should be displayed.
4. "Display results in separate categories" = yes, Default search category = Users, "Hide All results category" = yes: global search results should be spit by 4 tabs (Course content, Courses, Users, Other).  When a user search initially, Users tab should be displayed.
5. If a user modify URL and set "cat" to not existing category (e.g. &cat=bla-bla-courses), result should be displayed from the Default search category.

Assigning categories by plugin

Also as the patch introduces a new call back "search_area_categories" probably we'd like to test that it works as well:

1. Add a the following callback to mod/forum/lib.php:

   function forum_search_area_categories() {

   $categories = [];

   $categories[] = new \core_search\area_category(

   'test-1',

   'Test1',

   0,

   \core_search\manager::get_search_areas_list(true)

   );

   $categories[] = new \core_search\area_category(

   'test-2',

   'Test2',

   10,

   [\core_search\manager::get_search_areas_list(true)['mod_forum-post']]

   );

   return $categories;

   }

2. Search for some word that is present in your forum posts.
3. Check if the new categories appear on the search screen
4. Check if new categories appear in the Default search category select @ admin.
5. Check if new categories are displayed in the search areas table (/admin/searchareas.php) and they are associated to correct areas:
   1. 'Test1' is shown in all areas.
   2. 'Test2' is only shown in forum posts area.