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* Update outdated readme info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

website/package.json

@@ -13,8 +13,8 @@
 	"scripts": {
 		"postinstall": "node .build-scripts/install.ts",
 		"generate-editor-structure": "node .build-scripts/generate-editor-structure.ts generated/hierarchical_message_system_tree.txt generated/hierarchical_message_system_tree.html",
-		"lint": "eslint . && tsc --noEmit",
-		"lint-fix": "eslint . --fix && tsc --noEmit"
+		"check": "tsc --noEmit && eslint",
+		"fix": "eslint --fix"
 	},
 	"devDependencies": {
 		"@eslint/compat": "^2.0.1",