Fix data loss when switching from inline to side-by-side view on MR creation page

Insight

When switching from the inline to side-by-side code comparison at the bottom of the create merge request page, the page gets refreshed, the user is directed back to the top of the page, and any other information on the page is lost.

Supporting evidence

During the Q1FY23 Create stage benchmarking study, this was encountered by over a dozen users during the 'confirm proposed changes' task.

When I change this, it takes me back to the top of the page, which is a bit confusing...I would ideally prefer to stay here only. – S-15

Action

• Do not trigger a refresh, redirection, or incur data loss when switching between inline and side-to-side views on the MR creation page.

Resources

• 🕊 Dovetail project
• 🔍 Research issue
• 👣 Follow-up issue or epic

Proposal

• Make the inline/parallel mode reload the Changes portion by re-requesting the diffs HTML from the server