Add a checkered background to transparent artboards and the infinite canvas (#4022)

* Add checkered transparency rendering to infinite canvas and artboards

* Enable artboard clipping by default

* Make new infinite canvas documents begin with a white background layer

* Remove the export dialog's transparency option now that it's redundant

* Make exporting transparent JPGs use white not black

* Code review

node-graph/libraries/application-io/src/lib.rs

@@ -112,7 +112,6 @@ pub struct RenderConfig {
 	#[serde(alias = "view_mode")]
 	pub render_mode: RenderMode,
 	pub export_format: ExportFormat,
-	pub hide_artboards: bool,
 	pub for_export: bool,
 	pub for_eyedropper: bool,
 }