Merge request changes tab shows 0 until clicked or refreshed

Problem to solve

With the changes in !100390 (merged) we now load MR diffs asynchronously. this improves the performance substantially but leads to a bit of confusion since we show the changes as 0 prior to loading the content.

Proposal

We should consider optimistically loading the counts of changes and commits when the merge request is created. These counts are already present on the merge request creation page.