Restore option to load assembly into the current AppDomain

[ajcvickers]

This is to allow EF Core to update to a newer version of the package: see dotnet/efcore#32385

I will put up a PR that I have tested works for EF Core. I'll be happy to change the PR in whatever way is necessary to keep in line with the intent of the library. I'm hoping a new package can be published with this change so that we can patch EF Core in February with a dependency on the new version.