feat: extend DuplicateFilemask to operate on files

[nijel]

Proposed changes

Reusing filemask does not have to be the only issue, the very same issue can happen when a signle file from one component is reused as source for other component.

This also avoids special-casing this single alert and it now uses generic alerts interface.

Fixes #13259

Checklist

• Lint and unit tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added documentation to describe my feature.
• I have squashed my commits into logic units.
• I have described the changes in the commit messages.

Other information

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.95%. Comparing base (cc4b888) to head (deff8f0).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
weblate/trans/models/alert.py	90.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13302   +/-   ##
=======================================
  Coverage   90.95%   90.95%           
=======================================
  Files         603      603           
  Lines       62472    62495   +23     
  Branches     6456     6459    +3     
=======================================
+ Hits        56819    56841   +22     
+ Misses       3977     3976    -1     
- Partials     1676     1678    +2     

Files with missing lines	Coverage Δ
weblate/trans/models/__init__.py	94.23% <100.00%> (ø)
weblate/trans/models/component.py	80.48% <100.00%> (-0.08%)	⬇️
weblate/trans/tests/test_alert.py	100.00% <100.00%> (ø)
weblate/trans/models/alert.py	90.71% <90.00%> (-0.06%)	⬇️

... and 2 files with indirect coverage changes