convert settings to do/did action pattern

src/settings/index.ts

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2021 The Pybricks Authors
+
+// Definitions for user settings.
+
+export enum SettingId {
+    ShowDocs = 'showDocs',
+    DarkMode = 'darkMode',
+}
+
+export function getDefaultBooleanValue(id: SettingId): boolean {
+    switch (id) {
+        case SettingId.ShowDocs:
+            return window.innerWidth >= 1024;
+        case SettingId.DarkMode:
+            return false;
+        default:
+            throw Error(`Bad setting id: ${id}`);
+    }
+}