Fix FFmpeg version fallback parsing

[jonoomph]

Update FindFFmpeg.cmake to read component version defines from both version_major.h and version.h. Newer FFmpeg releases moved some version macros into version_major.h, which broke fallback detection when pkg-config did not provide component versions.

Fixes #947

[jonoomph]

FFMpeg Integration - parse_lib_version issue

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.28%. Comparing base (fbc37e2) to head (eb2411e).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1072      +/-   ##
===========================================
+ Coverage    70.11%   70.28%   +0.16%     
===========================================
  Files          241      241              
  Lines        29059    29497     +438     
===========================================
+ Hits         20375    20732     +357     
- Misses        8684     8765      +81     

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