fix: Use provided references for search of dependencies in AssemblyCompilations

[Herrmel]

Use provided references for search of dependencies in AssemblyCompilations.

This should resolve my issue in #10423.

Since I did not get any feedback on how best resolve the issue I thought maybe this would get some attention. What this approach does is basicly use the provided Metadatareferences and use their filepaths (if present) to help resolve dependencies via filenames for those that are not found by default.

I also included a small code duplication cleanup, I hope thats also ok.

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 79.33%. Comparing base (fe673ec) to head (7e94ee7).
Report is 502 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Docfx.Dotnet/CompilationHelper.cs	60.00%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10491      +/-   ##
==========================================
+ Coverage   74.31%   79.33%   +5.01%     
==========================================
  Files         536      547      +11     
  Lines       23189    23634     +445     
  Branches     4056     4066      +10     
==========================================
+ Hits        17234    18751    +1517     
+ Misses       4853     3711    -1142     
- Partials     1102     1172      +70     

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