Refactor the TypeScript data flow for full type safety and auto-generation of Rust types (#3865)

* Migrate Specta to Tsify to auto-generate messages.ts, working except colors and widgets

* Adopt the generated FillColor/Color/GradientStops

* Fix widget typing

* Separate WidgetGroup enum variants into wrapper structs

* Small rename

* Simplify widgets further

* Clean up message type references

* Switch type imports to the auto-generated file

* Remove lowercase serde rename

* Fix FillChoice deserialization

* Fix small regression from #3837

* Improve type safety

* Make WidgetSpan type-safe

* More cleanup and type safety

* More type safety

* More type safety

* Get the rest to type-check without errors; improve widget builder macro to have optional icons; improve Svelte 5 configs

* Cargo fmt

* Fix imports

* Update outdated readme info

* Fix lint command rename references

* Fix typos

* One more typos fix

* Remove unnecessary dep: prefix from the edited Cargo.toml files

* Remove excess parts from Cargo.toml

* Fix compiling on desktop

* Revert "Remove excess parts from Cargo.toml"

This reverts commit 6b711117b3a5d5d8a3ee20f36a43bc74930b7c82.

* Update dev docs with simpler, more accurate instructions

editor/src/messages/menu_bar/menu_bar_message_handler.rs

@@ -76,7 +76,7 @@ impl LayoutHolder for MenuBarMessageHandler {
 			TextButton::new("Graphite")
 				.label("")
 				.flush(true)
-				.icon(Some("GraphiteLogo".into()))
+				.icon("GraphiteLogo")
 				.on_commit(|_| FrontendMessage::TriggerVisitLink { url: "https://graphite.art".into() }.into())
 				.widget_instance(),
 			#[cfg(target_os = "macos")]
@@ -750,6 +750,6 @@ impl LayoutHolder for MenuBarMessageHandler {
 				.widget_instance(),
 		];
 
-		Layout(vec![LayoutGroup::Row { widgets: menu_bar_buttons }])
+		Layout(vec![LayoutGroup::row(menu_bar_buttons)])
 	}
 }