Fix snack bar not displayed in MediaViewer

[bmarty]

Content

The SnackBar was not displayed in the MediaViewer because it's in a Node which is displayed in Overlay mode. In this case, the Screen below (Messages or Gallery) is consuming the SnackBar. Using a local SnackbarDispatcher in MediaViewerPresenter fixes the issue. This is commit d36b413

c3e148b is closing the bottom sheet once an action is selected, to either leave space for the share native bottom sheet or the "saved" snackbar.

Other commits are cleanup.

Motivation and context

Closes #4128

Screenshots / GIFs

SaveSnackBar.mp4

Tests

• Open an image and save it to disk.
• You should see a confirmation snackbar.

Tested devices

• Physical
• Emulator
• OS version(s):

Checklist

• Changes have been tested on an Android device or Android emulator with API 24
• 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
• You've made a self review of your PR

[github-actions]

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[sonarqubecloud]

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 SonarQube Cloud

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 83.35%. Comparing base (3668e86) to head (c3e148b).
Report is 8 commits behind head on develop.

Files with missing lines	Patch %	Lines
.../designsystem/utils/snackbar/SnackbarDispatcher.kt	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #4195   +/-   ##
========================================
  Coverage    83.35%   83.35%           
========================================
  Files         1886     1886           
  Lines        49403    49404    +1     
  Branches      5804     5804           
========================================
+ Hits         41180    41181    +1     
  Misses        6134     6134           
  Partials      2089     2089           

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[ganfra]

Thanks for the changes, LGTM