Bug 1600267: part 8) Call `ComparePoints` instead of...

Bug 1600267: part 8) Call `ComparePoints` instead of `ComparePoints_Deprecated` in Selection. r=smaug

Some calls to `ComparePoints_Deprecated` remain, because adapting them
would require to add boilerplate code, which potentially will be deleted
again once `ComparePoints` supports crossing the Shadow DOM boundary.

Differential Revision: https://phabricator.services.mozilla.com/D57615

--HG--
extra : moz-landing-system : lando