Changed collapsed assignee tooltip to users name

## What does this MR do?

- Changes the collapsed assignee tooltip the users name rather than the username
- Updates the tooltip after updating the assignee

## What are the relevant issue numbers?

Closes #19280, #19281

## Screenshots (if relevant)

![Screen_Shot_2016-06-28_at_17.55.52](/uploads/e6ccc1703f59966c978e731a841aabdc/Screen_Shot_2016-06-28_at_17.55.52.png)

See merge request !4976