Vue initialization and FloatingMenu codebase refactoring and cleanup (#649)

* Clean up Vue initialization-related code

* Rename folder: dispatcher -> interop

* Rename folder: state -> providers

* Comments and clarification

* Rename JS dispatcher to subscription router

* Assorted cleanup and renaming

* Rename: js-messages.ts -> messages.ts

* Comments

* Remove unused Vue component injects

* Clean up coming soon and add warning about freezing the app

* Further cleanup

* Dangerous changes

* Simplify App.vue code

* Move more disparate init code from components into managers

* Rename folder: providers -> state-providers

* Other

* Move Document panel options bar separator to backend

* Add destructors to managers to fix HMR

* Comments and code style

* Rename variable: font -> font_file_url

* Fix async font loading; refactor janky floating menu openness and min-width measurement; fix Vetur errors

* Fix misaligned canvas in viewport until panning on page (re)load

* Add Vue bidirectional props documentation

* More folder renaming for better terminology; add some documentation

frontend/src/state-providers/fullscreen.ts

@@ -0,0 +1,47 @@
+import { reactive, readonly } from "vue";
+
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
+export function createFullscreenState() {
+	const state = reactive({
+		windowFullscreen: false,
+		keyboardLocked: false,
+	});
+
+	function fullscreenModeChanged(): void {
+		state.windowFullscreen = Boolean(document.fullscreenElement);
+		if (!state.windowFullscreen) state.keyboardLocked = false;
+	}
+
+	async function enterFullscreen(): Promise<void> {
+		await document.documentElement.requestFullscreen();
+
+		if (keyboardLockApiSupported) {
+			// eslint-disable-next-line @typescript-eslint/no-explicit-any
+			await (navigator as any).keyboard.lock(["ControlLeft", "ControlRight"]);
+			state.keyboardLocked = true;
+		}
+	}
+
+	async function exitFullscreen(): Promise<void> {
+		await document.exitFullscreen();
+	}
+
+	async function toggleFullscreen(): Promise<void> {
+		if (state.windowFullscreen) await exitFullscreen();
+		else await enterFullscreen();
+	}
+
+	// Experimental Keyboard API: https://developer.mozilla.org/en-US/docs/Web/API/Navigator/keyboard
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
+	const keyboardLockApiSupported: Readonly<boolean> = "keyboard" in navigator && (navigator as any).keyboard && "lock" in (navigator as any).keyboard;
+
+	return {
+		state: readonly(state) as typeof state,
+		fullscreenModeChanged,
+		enterFullscreen,
+		exitFullscreen,
+		toggleFullscreen,
+		keyboardLockApiSupported,
+	};
+}
+export type FullscreenState = ReturnType<typeof createFullscreenState>;