See https://gitlab.com/gitlab-org/gitlab-ce/issues/39118

Conflicts:
	app/views/ci/variables/_form.html.haml
	app/views/ci/variables/_table.html.haml
	ee/app/views/ci/variables/_environment_scope.html.haml
	spec/javascripts/ci_variable_list/ci_variable_list_ee_spec.js
	spec/javascripts/fixtures/projects.rb

- Change button group width on mobile to 100%
- Added scrolling container to activity top area secondary navigation
- Added bottom border to top-area nav-links to separate them from nav-controls

Part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/4110

Remove duplicate ee code

This was generalized for usage in the new variable table design, see
https://gitlab.com/gitlab-org/gitlab-ce/issues/39118#note_53615249

Conflicts:
	app/assets/stylesheets/pages/projects.scss
	ee/app/assets/javascripts/protected_branches/protected_branch_create.js
	ee/app/assets/javascripts/protected_tags/protected_tag_create.js
	ee/app/views/projects/protected_branches/ee/_dropdown.html.haml

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/41491

Closes #41561