[PM-5539] Migrate ThemingService (#8219)

* Update ThemingService

* Finish ThemingService

* Lint

* More Tests & Docs

* Refactor to ThemeStateService

* Rename File

* Fix Import

* Remove `type` added to imports

* Update InitServices

* Fix Test

* Remove Unreferenced Code

* Remove Unneeded Null Check

* Add Ticket Link

* Add Back THEMING_DISK

* Fix Desktop

* Create SYSTEM_THEME_OBSERVABLE

* Fix Browser Injection

* Update Desktop Manual Access

* Fix Default Theme

* Update Test

apps/desktop/src/platform/utils/from-ipc-system-theme.ts

@@ -0,0 +1,15 @@
+import { defer, fromEventPattern, merge } from "rxjs";
+
+import { ThemeType } from "@bitwarden/common/platform/enums";
+
+/**
+ * @returns An observable watching the system theme via IPC channels
+ */
+export const fromIpcSystemTheme = () => {
+  return merge(
+    defer(() => ipc.platform.getSystemTheme()),
+    fromEventPattern<ThemeType>((handler) =>
+      ipc.platform.onSystemThemeUpdated((theme) => handler(theme)),
+    ),
+  );
+};