Add grid snapping to graph imports/exports; improve layer panel drag into/between insertion; better preserve graph space on reordering (#1911)

* Fix disconnecting root node when previewing

* Final previewing fixes

* Improve positioning when moving layer to stack

* Improve layer panel

* Import/Export edge grid snapping

* Fix layer ordering and positioning

* Small bug fixes and improvements

* Fix copy and paste position

* Nit

* Align imports/edges when using scrolling

* Fix misaligned exports in demo artwork

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Co-authored-by: Keavon Chambers <keavon@keavon.com>

frontend/src/components/panels/Document.svelte

@@ -514,6 +514,7 @@
 					handlePosition={scrollbarPos.x}
 					on:handlePosition={({ detail }) => panCanvasX(detail)}
 					on:pressTrack={({ detail }) => pageX(detail)}
+					on:pointerup={() => editor.handle.setGridAlignedEdges()}
 				/>
 			</LayoutRow>
 		</LayoutCol>