`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.
Major changes included:
- better support for screen readers
- trapping focus in modals
- better tabbing order in composer
- alerts on no content found/number of items found
- better autofocus in modals
- mini-tag-chooser is now a multi-select component
- each multi-select-component will now display selection on one row
This reverts commit 20780a1eeed56b321daf18ee6bbfe681a51d1bf4.
* SECURITY: re-adds accidentally reverted commit:
03d26cd6: ensure embed_url contains valid http(s) uri
* when the merge commit e62a85cf was reverted, git chose the 2660c2e2 parent to land on
instead of the 03d26cd6 parent (which contains security fixes)
