.NET Core Support

Following the tutorial on the website to create a simple helloworld, I failed, and after looking through the related issues and PRs I finally got it transpiled, but still the generated project csproj file was in the old Visual Studio dependant style, which is certainly not working with .NET Core SDK building. I realized hxcs not supporting .NET Core yet.

But note that .NET Framework has been archived with its final version 4.8, then .NET Core (will be called '.NET' version 5 in the future) becomes the unique officially supported .NET implementation. Therefore by a certain day in the future, not supporting .NET Core equals to not supporting .NET.

As most companies have turned to use .NET Core, abandoning .NET Framework in their new projects, not supporting .NET Core is a critical reason that they would not take Haxe for their .NET stacks.

Thus I do think hxcs should pay all attention to support .NET Core, or Haxe would be no longer taken as a language that targets .NET.

Start with the website helloworld tutorial and inspect how hxcs generates the project .csproj file. Reproduce the SDK build failure, then define the work needed for the generated project to use the .NET Core SDK style and verify that the tutorial project builds successfully.

Written by the indexing model from the issue text.