Add descriptions to ambiguous links for screen readers (#7310)

* add title to room share link

Signed-off-by: Kerry Archibald <kerrya@element.io>

* add ExternalLink component

Signed-off-by: Kerry Archibald <kerrya@element.io>

* unit test ExternalLink

Signed-off-by: Kerry Archibald <kerrya@element.io>

* default target and rel for external link

Signed-off-by: Kerry Archibald <kerrya@element.io>

* use scss $font variables

Signed-off-by: Kerry Archibald <kerrya@element.io>

src/components/views/elements/ExternalLink.tsx

@@ -0,0 +1,36 @@
+/*
+Copyright 2021 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, { DetailedHTMLProps, AnchorHTMLAttributes } from 'react';
+import classNames from 'classnames';
+
+interface Props extends DetailedHTMLProps<AnchorHTMLAttributes<HTMLAnchorElement>, HTMLAnchorElement> {}
+
+/**
+ * Simple link component that adds external link icon after link children
+ */
+const ExternalLink: React.FC<Props> = ({ children, className, ...rest }) =>
+    <a
+        target="_blank"
+        rel="noreferrer noopener"
+        {...rest}
+        className={classNames('mx_ExternalLink', className)}
+    >
+        { children }
+        <i className='mx_ExternalLink_icon' />
+    </a>;
+
+export default ExternalLink;