Include inviter in the notification for invitation

[bmarty]

Content

Include the sender name (or id) in the notification for invitation.

Second commit is test cleanup.

Motivation and context

More useful notification

Screenshots / GIFs

Before	After

Note: rendering on iOS:

Tests

• Get invited to a room or to a DM and observe the content of the notification

Tested devices

• Physical
• Emulator
• OS version(s):

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]

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[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

All modified and coverable lines are covered by tests ✅

Project coverage is 82.67%. Comparing base (dfe9323) to head (6fc801e).
Report is 32 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3503   +/-   ##
========================================
  Coverage    82.67%   82.67%           
========================================
  Files         1731     1731           
  Lines        40844    40852    +8     
  Branches      4968     4968           
========================================
+ Hits         33768    33775    +7     
  Misses        5315     5315           
- Partials      1761     1762    +1     

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