Visual Studio Code Repeat shot cut key:

I am going to keep it short and sweet here. To duplicate a line simply put your cursor on the line you want repeated then hit these magic keyboard keys:

alt+shift+ up or down

You will see the magic begin.

Note, this works on Version 1.44.2 as of April 2020

BONUS:

Repeat each line as text entered as many lines as you want:
ctr+alt+shift+ up or down