Detect mime type when picking a file

[bmarty]

Content

The file picker will now try to detect the mime type of the selected file.
If it cannot be detected, it will fallback to application/octet-stream.

Motivation and context

Fixes #5254

Screenshots / GIFs

Tests

• In a timeline, click on the add attachment button
• select an audio file
• observe that the preview is now the preview of an audio file.
• If you send the file, it will be sent as an audio attachment and clients should render it as an audio file

The fix will also apply to other attachments, such as image and video.

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

❌ Patch coverage is 14.28571% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.64%. Comparing base (f852fb4) to head (5ffd5b8).
⚠️ Report is 13 commits behind head on develop.

Files with missing lines	Patch %	Lines
...braries/mediapickers/impl/DefaultPickerProvider.kt	0.00%	4 Missing ⚠️
...s/impl/messagecomposer/MessageComposerPresenter.kt	50.00%	0 Missing and 1 partial ⚠️
.../libraries/mediapickers/test/FakePickerProvider.kt	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5291      +/-   ##
===========================================
- Coverage    79.65%   79.64%   -0.01%     
===========================================
  Files         2258     2258              
  Lines        62491    62493       +2     
  Branches      7830     7832       +2     
===========================================
- Hits         49776    49775       -1     
- Misses        9849     9851       +2     
- Partials      2866     2867       +1     

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[ganfra]

LGTM, thanks!