Oct 1, 2020: 1.22 release

Flutter 1.22 is live! For details, see
Announcing Flutter 1.22.

Docs updated or added to flutter.dev since the 1.20 release

Updated the Developing for iOS 14 page with
details about targeting iOS 14 with Flutter, including some
Add-to-App, deep linking, and notification considerations.

Added a page on how to add an iOS App Clip,
a new iOS 14 feature that supports running lightweight,
no-install apps under 10 MB.

Added a page that describes how to migrate your app to use the
new icon glyphs available in
CupertinoIcons.