Allow continuous movement with Alt+Up / Alt+Down in script editor

[rogeriodec]

Godot version:
3.1

OS/device including version:
Windows 10 x64

Issue description:
When I want to move a line, up and down, inside the editor, when I press, for example, Alt+Up, it moves just 1 line.
In any other editors, if a keep it pressed, it continues to move the line.
But in the current editor, if I want to move 10 lines, I have to press Alt+Up 10 times.

Steps to reproduce:

Select one line, keep Alt+Up or Alt+Down pressed and it will move the line just 1 time.

[KoBeWi]

This was resolved as a side-effect of #28787