Previously the merge request widget would use the `updated_at` date as
the tooltip text for both closed & merged states. This is incorrect as
the `updated_at` date is actually changed when a user updates merge
request through commenting, description changes or anything else.

The widget states for merged & closed events now use their own event
object which holds their own `updated_at` date string. Also this text
has been correctly formatted through our date utilities to correctly
display the right timezone data in a user friendly way.

Closes #38545