Convert BlazorExtension to SDK style project

[pranavkm]

Fixes #7135

[pranavkm]

The vsixmanifest has the right version - <Identity Id="Microsoft.VisualStudio.BlazorExtension" Version="16.0.424242.424242" Language="en-US" Publisher="Microsoft" /> and the assembly metadata looks right:

[assembly: CompilationRelaxations(8)]
[assembly: RuntimeCompatibility]
[assembly: Debuggable()]
[assembly: TargetFramework(".NETFramework,Version=v4.7.2")]
[assembly: AssemblyMetadata("BuildNumber", "t000")]
[assembly: AssemblyMetadata("CommitHash", "5e5904dc6571c8f7bbc4ab9d5f1274ec40520195")]
[assembly: AssemblyMetadata("SourceCommitUrl", "https://github.com/aspnet/AspNetCore/tree/5e5904dc6571c8f7bbc4ab9d5f1274ec40520195")]
[assembly: AssemblyMetadata("Serviceable", "True")]
[assembly: AssemblyCompany("Microsoft Corporation.")]
[assembly: AssemblyConfiguration("Debug")]
[assembly: AssemblyCopyright("© Microsoft Corporation. All rights reserved.")]
[assembly: AssemblyFileVersion("0.8.0.42424")]
[assembly: AssemblyInformationalVersion("16.0.424242.424242")]
[assembly: AssemblyProduct("Microsoft ASP.NET Core")]
[assembly: AssemblyTitle("Microsoft.VisualStudio.BlazorExtension")]
[assembly: NeutralResourcesLanguage("en-US")]
[assembly: AssemblyVersion("0.8.0.0")]

Is there anything else that I'm missing here?

[natemcmaster]

Does debugging work in VS 2019? I was under the impression the VSIX tooling didn't support this project style yet.

[pranavkm]

@natemcmaster made some tweaks, which makes Ctrl-F5 \ debugging work.

[natemcmaster]

Nice 😎

[natemcmaster]

I don't know as much @rynowak about how VSIX stuff is supposed to work. Added a few minor comments, but as long as it works.

[natemcmaster]

Not 100% sure, but I think this Microsoft.NET.Sdk sets this to portable. Not sure if that's important or not.

[pranavkm]

Checked the Razor vsix, and it produces portable pdbs:

Guess it doesn't matter.