keyboard support to move nodes handles

[Birdsaregood]

When I click a node, I see handles which let me adjust the curve of the
line around the node. Please make it so we can select one of these handles
and move it with the keyboard so as to be able to make symmetrical effects.

[nightrow (jb-benoit)]

Maybe a dupe of #168432 - Cursor keys don't move special nodes - ?

[birdsaregood (ariel36)]

There are nodes which can be moved by the keyboard. However, when you click a node and see handles for the node come up which let you adjust the curve, you can't click these round handles to adjust with the keyboard. But if you could move it with the keyboard, then you would be able to make symmetrical edits to the curves.