Instance tables refactor part 1: wrap graphical data in the new Instances<T> struct (#2230)

* Port VectorData to Instances<VectorData>

* Port ImageFrame<P> and TextureFrame to Instances<ImageFrame<P>> and Instances<TextureFrame>

* Avoid mutation with the TransformMut trait

* Port GraphicGroup to Instances<GraphicGroup>

* It compiles!

* Organize debugging

* Document upgrading

* Fix Brush node

* Restore TransformMut in lieu of TransformSet trait

* Fix tests

* Final code review

editor/src/messages/tool/tool_messages/artboard_tool.rs

@@ -372,7 +372,7 @@ impl Fsm for ArtboardToolFsmState {
 					responses.add(GraphOperationMessage::NewArtboard {
 						id,
 						artboard: graphene_core::Artboard {
-							graphic_group: graphene_core::GraphicGroup::EMPTY,
+							graphic_group: graphene_core::GraphicGroupTable::default(),
 							label: String::from("Artboard"),
 							location: start.round().as_ivec2(),
 							dimensions: IVec2::splat(1),

editor/src/messages/tool/tool_messages/path_tool.rs

@@ -502,7 +502,7 @@ impl PathToolData {
 					});
 
 					// Make handles colinear if opposite handle is zero length
-					if opposite_handle_length.map_or(false, |l| l == 0.) {
+					if opposite_handle_length == Some(0.) {
 						shape_editor.convert_selected_manipulators_to_colinear_handles(responses, document);
 						return true;
 					}