Additional System.Web compatibility

[IanKemp]

• Not sure how to test instance members of HttpContext as the types required by its constructor aren't implemented yet. Should I just go and implement all dependencies as no-ops? Just dummied what I needed anyway.
• GenAPI treats GeneratePlatformNotSupportedAssemblyMessage as a literal string not a symbol (https://github.com/dotnet/arcade/blob/master/src/Microsoft.DotNet.GenAPI/build/Microsoft.DotNet.GenAPI.targets#L103), therefore the generated System.Web.notsupported.cs does throw new PlatformNotSupportedException("Strings.PlatformNotSupportedSystemWeb") instead of the intended throw new PlatformNotSupportedException(Strings.PlatformNotSupportedSystemWeb)

cc @ericstj

[ericstj]

GenAPI treats GeneratePlatformNotSupportedAssemblyMessage as a literal string not a symbol (https://github.com/dotnet/arcade/blob/master/src/Microsoft.DotNet.GenAPI/build/Microsoft.DotNet.GenAPI.targets#L103), therefore the generated System.Web.notsupported.cs does throw new PlatformNotSupportedException("Strings.PlatformNotSupportedSystemWeb") instead of the intended throw new PlatformNotSupportedException(Strings.PlatformNotSupportedSystemWeb)

I see, looks like I need to rename the resources type: https://github.com/dotnet/arcade/blob/d6dd7a000fe9908e4caae5eb9aa30ecc9cb917ff/src/Microsoft.Cci.Extensions/Writers/CSharp/CSDeclarationWriter.Methods.cs#L312-L319

[ericstj]

Thanks for the contribution. I went ahead and merged the change after fixing it up. Let me know if the new library works for you.