To .Net 5

[CommCody]

I'm trying to upgrade your playground to .net 5, I'm hitting two issues:

1. the css has changed and I've tried to fix it, but it's not exactly right
2. The loading of the assemblies to get the MetadataReference needs changing because Location on the assemblies is now an empty string, I've worked around this by assuming that the Name of the assembly is the name of the dll on disk.
3. I've had to change the csproj options to ensure the dlls get put on disk individually

I still have to do some cleanup, but if you could already take a look?

[davidwengier]

Thanks for the PR, sorry I didn't look at this. I did a trial upgrade of another project (copied from this one originally) to .NET 5 in davidwengier/DecompilationDiffer#1 and ran into an issue, namely dotnet/runtime#43411, which blocks upgrading because Roslyn uses Parallel.For internally. Not sure whether the other changes in here somehow work around that (though I can't see how they would) but I think .NET 5 is not going to work for this project sadly. Will have to wait for .NET 6 if/when that issue gets fixed. Nevermind can work around it :)