Add INSendMessageIntent NSUserActivity support to the main App

[kloenk]

This allows for shortcuts and with merge of matrix-org/matrix-ios-kit#906 support for Siri suggestions to open the app.

This should not be dependent on matrix-org/matrix-ios-kit#906 but just has fewer functions without it.

Pull Request Checklist

• I read the contributing guide
• UI change has been tested on both light and dark themes, in portrait and landscape orientations and on iPhone and iPad simulators
• Pull request is based on the develop branch
• Pull request contains a changelog file in ./changelog.d
• Pull request includes screenshots or videos of UI changes
• Pull request includes a sign off

[kloenk]

Related to #3407 and #4710

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}