Move layouts definitions to backend and fix Firefox overlay scrollbars (#647)

* Fix two-axis scrollbars in scrollable regions on Firefox

* Move Document Mode dropdown to the backend; and related code cleanup

* Port the Layer Tree options bar layout to the backend

* Port the tool shelf to the backend

* Clean up initialization and wasm wrapper

* Fix crash

* Fix missing document bar

* Remove unused functions in api.rs

* Code review

* Tool initalisation

* Remove some frontend functions

* Initalise -> Init so en-US/GB doesn't have to matter :)

* Remove blend_mode and opacity from LayerPanelEntry

Co-authored-by: 0hypercube <0hypercube@gmail.com>

frontend/src/state/wasm-loader.ts

@@ -12,7 +12,7 @@ export async function initWasm(): Promise<void> {
 	// Skip if the wasm module is already initialized
 	if (wasmImport !== null) return;
 
-	// Separating in two lines satisfies typescript when used below
+	// Separating in two lines satisfies TypeScript
 	const importedWasm = await import("@/../wasm/pkg").then(panicProxy);
 	wasmImport = importedWasm;