[APICompat] AssemblyLoadErrors should not be saved as CompatDifference

[ViktorHofer]

sdk/src/ApiCompat/Microsoft.DotNet.ApiCompatibility/Mapping/AssemblyMapper.cs

Lines 139 to 145 in 8d4bc4a

	_assemblyLoadErrors.Add(new CompatDifference(
	side == ElementSide.Left ? assembly.MetadataInformation : MetadataInformation.DefaultLeft,
	side == ElementSide.Right ? assembly.MetadataInformation : MetadataInformation.DefaultRight,
	DiagnosticIds.AssemblyReferenceNotFound,
	string.Format(Resources.MatchingAssemblyNotFound, $"{symbol.ContainingAssembly.Name}.dll"),
	DifferenceType.Changed,
	symbol.ContainingAssembly.Identity.GetDisplayName()));

The assembly load errors are currently created per unresolved type forward. Try to find a more efficient way to determine if they are already stored.

It might not be useful to encode the left and right during an AssemblyLoadError and put that into a CompatDifference. APICompat currently emits the following in a situation where left exists but right is missing:

C:\git\runtime2\src\libraries\apicompat\ApiCompat.proj(84,5): API compatibility errors between 'left' (left) and 'net8.0/System.Data.dll' (right): [C:\git\runtime2\src\libraries\apicompat\ApiCompat.proj]
C:\git\runtime2\src\libraries\apicompat\ApiCompat.proj(84,5): error CP1002: Could not find matching assembly: 'System.Data.SqlClient.dll' in any of the search directories. [C:\git\runtime2\src\libraries\apicompat\ApiCompat.proj]

Based on that log it wasn't clear to me that this actually referred to the right hand side as the 'left' (left) entry confused me.

[ghost]

@dotnet/area-infrastructure-libraries a new issue has been filed in the ApiCompat area, please triage

[ViktorHofer]

This is completed.