Focus trap breaks on the root of an `ng-template` in an overlay

[jelbourn]

Reproduction

https://stackblitz.com/edit/angular-zgwmej?file=src%2Fapp%2Fapp.component.html

There seems to be a timing issue where the focus trap anchor elements are added to the DOM before the overlay element is moved into the overlay container, so those elements end up in the wrong place and don't capture anything.