navigation : clear backstack when opening room from outer node

[ganfra]

Content

Take over #3968

Reset the navigation to the room list level. This is the behaviour in most IM apps, and it seems more natural (tested this on WhatsApp, Telegram and also EXI).
The room is always added to the backstack, even if already stashed or active.

Motivation and context

Fixes #3098

Screenshots / GIFs

Tests

• Step 1
• Step 2
• Step ...

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

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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

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.

Project coverage is 83.05%. Comparing base (181cf56) to head (5ea8d57).
Report is 26 commits behind head on develop.

Files with missing lines	Patch %	Lines
...tlin/io/element/android/appnav/LoggedInFlowNode.kt	0.00%	18 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3984      +/-   ##
===========================================
+ Coverage    83.03%   83.05%   +0.02%     
===========================================
  Files         1796     1806      +10     
  Lines        45600    45656      +56     
  Branches      5375     5380       +5     
===========================================
+ Hits         37864    37921      +57     
+ Misses        5855     5848       -7     
- Partials      1881     1887       +6     

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[bmarty]

Tested OK! Thanks.