Add hotkey to move all child nodes when moving a node in the NodeGraph

[bentoogood]

Yuta has expressed interest in being able to quickly move all the nodes upstream of the selected node by holding some hotkey.

Here's a mock up of the behaviour:

This can be helpful when shuffling branches of a shader network around to make space.

[danieldresser]

Instead of holding a hotkey during dragging, could it just be a hotkey you press to select all upstream nodes of the current node? Then you just tap the key to get a selection, and then you can move it, or delete it, or duplicate it.

Also, for most of these cases, you probably wouldn't want all upstream nodes - you'd just want all upstream nodes that aren't upstream of anything outside the subtree you're selecting. ( ie. if iePrimVar2 was connected to ieCheckerBoard1, then we usually wouldn't want to select it.

[bentoogood]

( ie. if iePrimVar2 was connected to ieCheckerBoard1, then we usually wouldn't want to select it.

Disagree - in the original use case the user would want to move iePrimVar2 even if it was connected to ieCheckerBoard1

[johnhaddon]

I'm with Ben on the interpretation of upstreamness. And I think there's a good case for a "Select Upstream Nodes" menu item (there are similar items already in the Edit menu) regardless of whether or not we do this one.