Metadata interface updates

[jcmosc]

This makes the Swift refinement for OGTypeApplyFields a top level function to match the demangled signature:

AttributeGraph.forEachField(of: Any.Type, do: (Swift.UnsafePointer<Swift.Int8>, Swift.Int, Any.Type) -> ()) -> (),

[codecov]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 4.83%. Comparing base (65a976c) to head (2778ba9).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/OpenGraph/Runtime/Metadata.swift	0.00%	14 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #174      +/-   ##
========================================
- Coverage   4.89%   4.83%   -0.06%     
========================================
  Files         28      28              
  Lines        817     827      +10     
========================================
  Hits          40      40              
- Misses       777     787      +10     

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