msbuild should pass warning properties to GetReferenceNearestTargetFrameworkTask

[mishra14]

Came up while investigating NuGet/Home#7137 and #3546

Since NuGet is now throwing a warning in the GetReferenceNearestTargetFrameworkTask, msbuild should also pass warning properties like TreatWarningsAsErrors, WarningsAsErrors and NoWarn to enable full user experience.

[mishra14]

Given that msbuild has support for this as part of #1928, I would say this is not high priority.

But we should still do this work to keep a consistent way of warning properties.