Use UTType to determine correct content type

[nspassov]

• Use UTType to determine content type for .file() handlers
• Adjust minimum target versions
• Update unit tests

[codecov]

Codecov Report

❌ Patch coverage is 69.56522% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.17%. Comparing base (67105c3) to head (1d52ca6).
⚠️ Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
FlyingFox/Sources/Handlers/FileHTTPHandler.swift	69.56%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
- Coverage   94.56%   94.17%   -0.39%     
==========================================
  Files          62       62              
  Lines        4119     4138      +19     
==========================================
+ Hits         3895     3897       +2     
- Misses        224      241      +17     

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[swhitty]

Thank you! Just a few small changes to get the builds to pass for Swift 5

[swhitty]

I've tested this branch without this v11 change and all tests passed so we can remove this.

Then we can merge 🙏🏻

[swhitty]

Thanks!