[Uno.Core] Compiling error on Visual Studio 2019

[warrenbenyahia]

I'm submitting a...

Bug report (I searched for similar issues and did not find one)

Current behavior

• Following error appears when building the Uno.Core.csproj or Uno.Core.Build.csproj :

  1>C:\Users\warren.benyahia\.nuget\packages\msbuild.sdk.extras\1.6.68\Build\LanguageTargets\CheckMissing.targets(36,5): error : The specified language targets for uap10.0 is missing. Ensure correct tooling is installed for 'uap'. Missing: 'C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Microsoft\WindowsXaml\v16.0\Microsoft.Windows.UI.Xaml.CSharp.targets'

Expected behavior

Build successfully

Minimal reproduction of the problem with instructions

• Build Uno.Core.csproj or Uno.Core.Build.csproj

Environment

Nuget Package: 

Package Version(s): 
MSBuild.Sdk.Extras : 1.6.68

Affected platform(s):
- [ ] iOS
- [ ] Android
- [ ] WebAssembly
- [ ] Windows
- [x] Build tasks

Visual Studio
- [x] 2019 (version: 16.3.4)
- [ ] 2017 Preview (version: )
- [ ] for Mac (version: )

Relevant plugins
- [ ] Resharper (version: )

[jeromelaban]

This will need to be adjusted along with the move to VS2019, with unoplatform/uno#1867