Sync `show whitespace changes in diffs` user preference
Problem to Solve
As explained in &5713 (comment 563998664), the Show whitespace changes in diffs
user preference exists in two places, but those are not in sync:
- User preferences page
- MR preferences menu
Changing the preference in the MR menu will always override what is set in the user preferences page.
Proposal
Having backend create the API endpoint for this user preference and then on the MR having it use that API to actually toggle the preference.
This feature falls apart the moment someone tries to use a different computer, clears their cookies, opens in a new browser, etc. By leveraging an API to do this, we can provide a more consistent experience to users across these situations.
Edited by Pedro Moreira da Silva