New theme ui in user settings (#12576)

* Add hook to get the theme

* Adapt subsection settings to new ui

* WIP new theme subsection

* Add theme selection

* Fix test types

* Disabled theme selector when system theme is used

* Update compound to `4.4.1`

* Add custom theme support

* Remove old ThemChoicePanel

* Fix QuickThemeSwitcher-test.tsx

* Fix AppearanceUserSettingsTab-test.tsx

* Update i18n

* Fix ThemeChoicePanel-test.tsx

* Update `@vector-im/compound-web`

* Small tweaks

* Fix CSS comments and use compound variable

* Remove custom theme title

* i18n: update

* test: add tests to theme selection

* test: update AppearanceUserSettingsTab-test snapshot

* test: rework custom theme

* playwright: fix audio-player.spec.ts

* playwright: appearance tab

* test: update snapshot

* playright: add custom theme

* i18n: use correct char for ellipsis

* a11y: add missing aria-label to delete button

* dialog: update close button tooltip

* theme: remove local state and handle custom delete

* theme: don't add twice the same custom theme

* test: update snapshot

* playwright: update snapshot

* custom theme: add background to custom theme list

* update compound web

* Use new destructive property on `IconButton` of theme panel

* test: update snapshots

* rename new ui into legacy

* remove wrong constructor doc

* fix theme selector padding

* theme selector: fix key

* test: fix e2e

src/hooks/useTheme.ts

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2024 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { SettingLevel } from "../settings/SettingLevel";
+import { useSettingValue, useSettingValueAt } from "./useSettings";
+
+/**
+ * Hook to fetch the current theme and whether system theme matching is enabled.
+ */
+export function useTheme(): { theme: string; systemThemeActivated: boolean } {
+    // We have to mirror the logic from ThemeWatcher.getEffectiveTheme so we
+    // show the right values for things.
+
+    const themeChoice = useSettingValue<string>("theme");
+    const systemThemeExplicit = useSettingValueAt<string>(SettingLevel.DEVICE, "use_system_theme", null, false, true);
+    const themeExplicit = useSettingValueAt<string>(SettingLevel.DEVICE, "theme", null, false, true);
+    const systemThemeActivated = useSettingValue<boolean>("use_system_theme");
+
+    // If the user has enabled system theme matching, use that.
+    if (systemThemeExplicit) {
+        return {
+            theme: themeChoice,
+            systemThemeActivated: true,
+        };
+    }
+
+    // If the user has set a theme explicitly, use that (no system theme matching)
+    if (themeExplicit) {
+        return {
+            theme: themeChoice,
+            systemThemeActivated: false,
+        };
+    }
+
+    // Otherwise assume the defaults for the settings
+    return {
+        theme: themeChoice,
+        systemThemeActivated,
+    };
+}