Device manager: generic settings subsection component (PSG-636) (#9147)

* add feature_new_device_manager labs flag

* add generic settings tab container

* settingstab section styles

* add session manager tab to user settings

* add sessions tab case to UserSettingDialog test

* fussy import ordering

* remove posthog tracking

* i18n

* add generic settings subsection component

src/components/views/settings/shared/SettingsSubsection.tsx

@@ -0,0 +1,37 @@
+/*
+Copyright 2022 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 React from "react";
+
+import Heading from "../../typography/Heading";
+
+export interface SettingsSubsectionProps {
+    heading: string;
+    description?: string | React.ReactNode;
+    children?: React.ReactNode;
+}
+
+const SettingsSubsection: React.FC<SettingsSubsectionProps> = ({ heading, description, children }) => (
+    <div className="mx_SettingsSubsection">
+        <Heading className="mx_SettingsSubsection_heading" size='h3'>{ heading }</Heading>
+        { !!description && <div className="mx_SettingsSubsection_description">{ description }</div> }
+        <div className="mx_SettingsSubsection_content">
+            { children }
+        </div>
+    </div>
+);
+
+export default SettingsSubsection;