Update dependencies from https://dev.azure.com/dnceng/internal/_git/dotnet-wpf-int build 20200817.2 (#3342)

[master] Update dependencies from dnceng/internal/dotnet-wpf-int
- Updates:
  - Microsoft.DotNet.Wpf.DncEng: from 5.0.0-rc.1.20414.3 to 5.0.0-rc.1.20417.2