Fix Document > Clear Artboards so it doesn't also clear everything else

[moOsama76]

Continuation of first attempt with unmerged PR #2015

[Keavon]

!build

[github-actions]

📦 Build Complete for fb422f7
https://28720137.graphite.pages.dev

[Keavon]

Problem: this introduces an intermediate history step which you'll see if you open the graph and undo three times to get back when it should have taken just one step.

Other minor problem: it seems that the Artboard layer gets replaced by a Merge layer but it ends up in a different position in the graph. Ideally this wouldn't cause the layers to shift. In a case with multiple artboards each containing layers, I'm finding this even results in things overlapping in the graph after running this which isn't a suitable outcome.

Thanks, and welcome back!

[Keavon]

!build

[github-actions]

📦 Build Complete for f6587ca
https://a35a885b.graphite.pages.dev

[Keavon]

Can you please make it add a Transform node, feeding into the replacement Merge node, if the artboard has a nonzero Location? Currently, all former artboards teleport to having a top-left location at the canvas origin since the artboard offset is lost.