Fixes merge request widget date tooltip inconsistencies
What does this MR do?
Previously the merged request widget merged & closed states where using the merge requests
updated_at date which is incorrect. This date is updated whenever the merge request is updated through comments, description changes etc.
Now the merged & closed states use their own event date which includes their own
updated_at dates. These dates are also correctly formatted through our
gl.utils date utility methods to create a user friendly tooltip text.
Screenshots (if relevant)
What are the relevant issue numbers?
Closes #38545 (closed)