Merge branch...

Merge branch '498297-add-comment-on-vue-transition-classes-so-that-we-do-not-accidently-remove-them-2' into 'master' 

Move all Vue transition classes into vue_transitions.scss

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/168752



Merged-by: Scott de Jonge <sdejonge@gitlab.com>
Approved-by: Scott de Jonge <sdejonge@gitlab.com>
Co-authored-by: James Rushford <jrushford@gitlab.com>