Allow short commit show to be selectable in merge request version dropdown

Problem to solve

Make the text inside the merge request version selectable for the commit sha
Example:

Intended users

All merge request developers

Further details

When someone rebases a merge request and force pushes I like to do a review of the changes made in the rebase. This requires the previous commit show before the force push. This versions dropdown contains that sha but it is impossible to copy. It only navigates you to the diff and even that doesn't contain the sha in the url or anywhere else. So I have to copy it manually key by key.

Proposal

Change the html and css for /app/assets/javascripts/diffs/components/compare_versions.vue to make only the short commit sha text selectable so people can copy it