Remove usages of gl-xs-flex-direction-column CSS util
This replaces usages of the desktop-first gl-xs-flex-direction-column CSS util with
mobile-first alternatives.
Screenshots or screen recordings
There is no visual change as we are essentially reproducing the same layouts but with mobile-first utils instead of desktop-first ones. Here are a few screenshots for reference.
Subject
Mobile
Desktop
Abuse report header
Abuse report content
Abuse report activity
Invite modal
File browser header
MR acceptance checklist
This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.
