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

test/components/views/settings/shared/SettingsSubsection-test.tsx

@@ -0,0 +1,45 @@
+/*
+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 { render } from '@testing-library/react';
+
+import SettingsSubsection from '../../../../../src/components/views/settings/shared/SettingsSubsection';
+
+describe('<SettingsSubsection />', () => {
+    const defaultProps = {
+        heading: 'Test',
+        children: <div>test settings content</div>,
+    };
+    const getComponent = (props = {}): React.ReactElement =>
+        (<SettingsSubsection {...defaultProps} {...props} />);
+
+    it('renders without description', () => {
+        const { container } = render(getComponent());
+        expect(container).toMatchSnapshot();
+    });
+
+    it('renders with plain text description', () => {
+        const { container } = render(getComponent({ description: 'This describes the subsection' }));
+        expect(container).toMatchSnapshot();
+    });
+
+    it('renders with react element description', () => {
+        const description = <p>This describes the section <a href='/#'>link</a></p>;
+        const { container } = render(getComponent({ description }));
+        expect(container).toMatchSnapshot();
+    });
+});