Improve the text for mentions and replies in notifications

[jmartinesp]

Content

When we receive a notification with a message that either mentions or replies to the current user - since we can't know if it mentioned or replied to, it's either both or none - instead of setting its text to Foo mentioned you: actual message we'll create a fake Person to display in the MessagingStyle for the notification, similar to what WhatsApp does.

Any other messages will be using the normal Person as they did until now, so they'll be grouped together.

Motivation and context

Counterpart of element-hq/element-x-ios#2397 for Android.

Screenshots / GIFs

Tests

• In some room, send a message that mentions or replies to some other account of yours where you have EXA installed.
• The notification should display as in the screenshot.
• If any other non-mention/reply messages are sent they should keep the current style.

Tested devices

• Physical
• Emulator
• OS version(s): 14

Checklist

• Changes have been tested on an Android device or Android emulator with API 23
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-x-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request title will be used in the release note, it clearly define what will change for the user
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR

[github-actions]

📱 Scan the QR code below to install the build (arm64 only) for this PR.

If you can't scan the QR code you can install the build via this link: https://i.diawi.com/95MH8o

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 82.74%. Comparing base (a942fd4) to head (ca174f6).
Report is 6 commits behind head on develop.

Files	Patch %	Lines
...mpl/notifications/factories/NotificationCreator.kt	44.44%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3328      +/-   ##
===========================================
- Coverage    82.74%   82.74%   -0.01%     
===========================================
  Files         1680     1680              
  Lines        39380    39388       +8     
  Branches      4778     4779       +1     
===========================================
+ Hits         32585    32590       +5     
- Misses        5117     5119       +2     
- Partials      1678     1679       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[bmarty]

Nice, thanks!