As of #23867 this is now a real package, so updating the imports to
use the real package name, rather than relying on the alias. The
name change in the package name is because `I18n` is not a valid
name as NPM packages must be all lowercase.
This commit also introduces an eslint rule to prevent importing from
the old I18n path.
For themes/plugins, the old 'i18n' name remains functional.
The unread(s) will still show in the sidebar, outside of chat and when in drawer mode. This is to prevent the confusion to show an unread count for chat on a button which is going to take the user out of chat.
This commit ensures we have correct icon and title on mobile for the chat header icon.
It also fixes a bug where the site setting was not correctly used when the user has not yet set the user option.
Both cases are now correctly tested.
