Include more dependencies in Microsoft.AspNetCore.App.nuspec

- all three come from CoreFx or core-setup

Author: dougbu

build/dependencies.props

@@ -230,5 +230,10 @@
     <XunitExtensibilityExecutionPackageVersion>2.3.1</XunitExtensibilityExecutionPackageVersion>
     <XunitPackageVersion>2.4.0</XunitPackageVersion>
     <XunitRunnerVisualStudioPackageVersion>2.4.0</XunitRunnerVisualStudioPackageVersion>
+
+    <!-- Dependencies listed only to include otherwise-transitive references in Microsoft.AspNetCore.App.nuspec. -->
+    <MicrosoftDotNetPlatformAbstractionsPackageVersion>2.1.0</MicrosoftDotNetPlatformAbstractionsPackageVersion>
+    <SystemSecurityCryptographyPkcsPackageVersion>4.5.0</SystemSecurityCryptographyPkcsPackageVersion>
+    <SystemTextEncodingCodePagesPackageVersion>4.5.0</SystemTextEncodingCodePagesPackageVersion>
   </PropertyGroup>
 </Project>

build/external-dependencies.props

@@ -222,6 +222,11 @@
     <ExternalDependency Include="xunit.extensibility.execution" Version="$(XunitExtensibilityExecutionPackageVersion)" />
     <ExternalDependency Include="xunit.runner.visualstudio" Version="$(XunitRunnerVisualstudioPackageVersion)" />
     <ExternalDependency Include="xunit" Version="$(XunitPackageVersion)" />
+
+    <!-- Dependencies listed only to include otherwise-transitive references in Microsoft.AspNetCore.App.nuspec. -->
+    <ExternalDependency Include="Microsoft.DotNet.PlatformAbstractions" Version="$(MicrosoftDotNetPlatformAbstractionsPackageVersion)" />
+    <ExternalDependency Include="System.Security.Cryptography.Pkcs" Version="$(SystemSecurityCryptographyPkcsPackageVersion)" />
+    <ExternalDependency Include="System.Text.Encoding.CodePages" Version="$(SystemTextEncodingCodePagesPackageVersion)" />
   </ItemGroup>
 
 </Project>