* infra: Migrate to .NET 5
This migrate projects and CI to .NET 5
* Remove language version restrictions (now on 9.0 by default)
* infra: pin .NET 5 to avoid later issues
* infra: Cleanup csproj files
* infra: update dependencies
* infra: Add temporary workaround for a bug in Vector128.Create
see https://github.com/dotnet/runtime/issues/44704 for more informations
Some parts of our code needs C# 8 who isn't set as default in Visual Studio. To fix this we have to set the C# version correctly in the csproj files and then we are be able to build the project using Visual Studio.
* Updated all NuGet packages to latest, and updated the framework from .NET Core 3.0 to 3.1.
* Updating appveyor settings for 3.1
Updating appveyor to use the netcoreapp3.1 path instead of 3.0.
* Removing unneeded NuGet package System.Runtime.CompilerServices.Unsafe.
* Removing unused NuGet package SharpFontCore.
* Removing unused NuGet package TimeZoneConverter.Posix
* Cleaning up by adding newline to a csproj.
* Simplfying a NuGet conditional include, and adding a warning disable for an annoying NuGet package.
* I'm not sure if .travis.yml is still used, but I'm updating its 'dotnet' version to the correct SDK.
* Making the runtime version into its own environment variable so it's a bit easier to change in the future.
* Removing OpenTK.NetStandard reference from Ryujinx.Common
* Fixing indentation in Common.csproj
* Updating the README to specify .NET Core 3.1.
* Reverting the update of the GTKSharp package so it doesn't block the PR.
