Issue #3369868 by seda12, Grimreaper: Move examples library links under appearance

ui_examples.links.menu.yml

+ui_suite.index:
+  title: 'UI libraries'
+  description: 'Design system libraries.'
+  route_name: ui_suite.index
+  parent: system.themes_page
+
 ui_examples.overview:
-  title: 'UI Examples library'
-  description: 'See a list of UI Examples which exist on the site.'
-  parent: system.admin_reports
+  title: 'Examples'
+  description: 'See a list of examples which exist on the site.'
   route_name: ui_examples.overview
+  parent: ui_suite.index

ui_examples.links.task.yml

+ui_suite.index:
+  title: 'UI libraries'
+  route_name: ui_suite.index
+  base_route: system.themes_page

ui_examples.routing.yml

+ui_suite.index:
+  path: '/admin/appearance/ui-libraries'
+  defaults:
+    _controller: '\Drupal\system\Controller\SystemController::systemAdminMenuBlockPage'
+    _title: 'UI libraries'
+  requirements:
+    _permission: 'access patterns page+access_ui_styles_library+access_ui_examples_library'
+
 ui_examples.overview:
   path: '/examples'
   defaults: