`discourse-common` was created in the past to share logic between the
'wizard' app and the main 'discourse' app. Since then, the wizard has
been consolidated into the main app, so the separation of
`discourse-common` is no longer useful.
This commit moves `discourse-common/(lib|utils)/*` into
`discourse/lib/*`, adds shims for the imports, and updates existing
uses in core.
This commit finalises the admin setting page consistency
efforts by:
* Converting all route templates into .gjs
* Adding `@hideTabs={{true}}` for all the page headers so we
don't show a border line when it's not needed
* Introduce `@showBreadcrumb` and default to true for
AdminAreaSettings, for all these pages the Settings part of
the breadcrumb is redundant
Followup c2282439b32d879a73217eec62449f042914d7d0
Make the Files and Other config pages reached from the sidebar
use our consistent site setting page rules.
Also slightly improves AdminAreaSettings so we don't show
"Settings not found" when still loading settings.
Setting tab should be added to permalinks so admins do not need to have left `/permalinks`.
A new component called `AreaSetting` was added to avoid duplications and
simplify adding settings to other sections.
