Angular 17 + Bootstrap 5.3 Upgrade

[Stephanie Leary]

Angular 17 is out and ng-bootstrap has updated to Bootstrap 5.3, so it's time for us to plan our upgrade. Ang17 includes faster builds and much better developer documentation, both of which I'm really looking forward to: https://blog.angular.io/introducing-angular-v17-4d7033312e4b

We will need to replace the accordion component first (bug 2025296).

We should also switch from CSS to Sass (bug 2030516) and move all our colors to variables (bug 2023449) if we want to take advantage of 5.3's support for multiple color modes (bug 1740529).

Other than accordions, there are not as many huge UI changes as there were in the original Bootstrap 5 upgrade (bug 2000482), so it should be less disruptive.