Sdk.Targets - Use GetTargetFrameworkIdentifier to identify framework.

[TheBrambleShark]

Example Input:

<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

    <PropertyGroup>
        <NetFx>net461</NetFx>
        <NetStandard>netstandard2.0</NetStandard>
        <NetCoreApp>netcoreapp3.0</NetCoreApp>
        <NetCore>net5.0</NetCore>
    </PropertyGroup>

    <Target Name="MyTarget">
        <Message Importance="high" Text="$(NetFx) = $([MSBuild]::GetTargetFrameworkIdentifier($(NetFx)))" />
        <Message Importance="high" Text="$(NetStandard) = $([MSBuild]::GetTargetFrameworkIdentifier($(NetStandard)))" />
        <Message Importance="high" Text="$(NetCoreApp) = $([MSBuild]::GetTargetFrameworkIdentifier($(NetCoreApp)))" />
        <Message Importance="high" Text="$(NetCore) = $([MSBuild]::GetTargetFrameworkIdentifier($(NetCore)))" />
    </Target>

</Project>

Example Output:

net461 = .NETFramework
netstandard2.0 = .NETStandard
netcoreapp3.0 = .NETCoreApp
net5.0 = .NETCoreApp

API Proposal:

<PropertyGroup>
  <RemoraFrameworkIdentifier>$([MSBuild]::GetTargetFrameworkIdentifier($TargetFramework))</RemoraFrameworkIdentifier>
  <IsNET>$(RemoraFrameworkIdentifier) == '.NETCoreApp'</IsNET>
  <IsNETCore>$(RemoraFrameworkIdentifier) == '.NETCoreApp'</IsNETCore>
  <IsNETStandard>$(RemoraFrameworkIdentifier) == '.NETStandard'</IsNETStandard>
  <IsNETFramework>$(RemoraFrameworkIdentifier) == '.NETFramework'</IsNETFramework>
  <IsRunnableTarget>$(RemoraFrameworkIdentifier) != '.NETStandard'</IsRunnableTarget>
</PropertyGroup>

Drawbacks:
We lose differentiation between IsNET and IsNETCore. I'm not too entirely sure what IsNET is used for though - MSBuild doesn't appear to differentiate between netcoreapp3.0 and net5. Additionally, it doesn't appear to be used within the SDK at all. Is this intended for use by consumers of the SDK?