Highlight empty lines

## What does this MR do?

Rather than just highlight the text, file line highlighting now highlights the full line including empty lines

## What are the relevant issue numbers?

Closes #19484 

## Screenshots (if relevant)

![Screen_Shot_2016-07-05_at_13.52.31](/uploads/d3bddc918d731681465381e96c0aa2b0/Screen_Shot_2016-07-05_at_13.52.31.png)

See merge request !5092