Fix room and user avatar downloaded with a .bin extension.

[bmarty]

Content

Let the SDK set a correct extension to downloaded file by providing a full mimetype when a base mimetype is available.

Motivation and context

Fixes #4803

Screenshots / GIFs

Tests

• Open a room avatar and downloaded it to the system.
• Observe that the extension of the downloaded file is no jpeg, it was bin previously.

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

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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

[jmartinesp]

I think this is doing what iOS does, assuming images are jpgs. At least, when I downloaded this image it appeared as .jpeg and when you open it with a hex editor you can see it's a PNG.

It's better than what we have, but I was thinking about something more like this option.

[bmarty]

It's better than what we have, but I was thinking about something more like this option.

Yes, I was thinking about that too, but here, it appears that it's the Rust SDK which downloads the file and decides of its extension based on the provided mime type. So I'd argue that this problem could be fixed SDK side.

In the meantime I think that this fix is enough as a first step. Do you agree?

[jmartinesp]

Yes, it's probably fine. Also, it seems like there are some very handy mime type libraries on Rust that could solve this problem instead of us re-implementing them ourselves. It's probably worth a shot doing it there.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 80.46%. Comparing base (3ba11db) to head (c704a47).
Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
...oid/libraries/matrix/impl/media/RustMediaLoader.kt	0.00%	7 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4830      +/-   ##
===========================================
- Coverage    80.47%   80.46%   -0.01%     
===========================================
  Files         2140     2140              
  Lines        56756    56762       +6     
  Branches      7110     7114       +4     
===========================================
  Hits         45672    45672              
- Misses        8649     8655       +6     
  Partials      2435     2435              

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