Sync up master with Ember CLI branch where possible (PR #11707)

These changes should all be safe to live in master even if they’re not being used yet.

GitHub

This pull request introduces 1 alert when merging c05c22d129b94160723a0a7d70db977b61275481 into 1ad378f5c5703857332613b2196000fe04e97135 - view on LGTM.com

new alerts:

  • 1 for Expression has no effect

Do we care about lgtm-com bot warning on this line?

yes, I’m pushing a fix.