ManagedLoadContext: Search In Additional Probing Paths (Fixes #162)

[Sewer56]

Not really sure what to say here.
This is an extremely minor simple fix for issue #162; that has been manually tested and sitting on my fork for a while.

I in particular remember using this in order to load the (Windows) desktop runtime inside a plugin; from a regular cross-platform console app compiled without the UseWindowsForms / UseWpf MSBuild Project properties. (Normally this would fail because default ALC wouldn't probe for desktop runtime as the runtimeconfig.json file wouldn't reference it.)

Of course in practice you probably shouldn't need to do this; it was just a tiny experiment of mine which was how I found the original bug in the first place IIRC.

I might add a unit test for this if I feel motivated; I think the easiest thing would be to have MSBuild copy a dependency (assembly) to a subdirectory then add a probing path to that directory inside the test; that would be one way to do it at least.

[natemcmaster]

LGTM! I'm just going to rebase this against the main branch and then merge.

[codecov]

Codecov Report

Merging #172 (3b7497d) into main (c6736c9) will increase coverage by 0.01%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##             main     #172      +/-   ##
==========================================
+ Coverage   81.85%   81.86%   +0.01%     
==========================================
  Files          15       15              
  Lines         540      546       +6     
==========================================
+ Hits          442      447       +5     
- Misses         98       99       +1     

Impacted Files	Coverage Δ
src/Plugins/Loader/ManagedLoadContext.cs	77.93% <78.57%> (+0.23%)	⬆️

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