When inferring @content/@none with copy to output, use full path

When doing P2P references, not using the full path causes the resulting package
to fail since the path is relative to the referenced project, rather than the
referencing one.

Author: kzu

src/Build/NuGet.Build.Packaging.Tasks/NuGet.Build.Packaging.Inference.targets

@@ -32,6 +32,9 @@ Copyright (c) .NET Foundation. All rights reserved.
 
 		<!-- Only default to true if the project isn't a nuget packaging project itself and its primary output is lib. -->
 		<IncludeFrameworkReferencesInPackage Condition="'$(IncludeFrameworkReferencesInPackage)' == '' and '$(IsPackagingProject)' != 'true' and '$(PrimaryOutputKind)' == 'Lib'">true</IncludeFrameworkReferencesInPackage>
+
+		<_OutputFullPath Condition="$([System.IO.Path]::IsPathRooted($(OutputPath)))">$(OutputPath)</_OutputFullPath>
+		<_OutputFullPath Condition="'$(_OutputFullPath)' == ''">$(MSBuildProjectDirectory)\$(OutputPath)</_OutputFullPath>
 	</PropertyGroup>
 
 	<PropertyGroup>
@@ -106,7 +109,7 @@ Copyright (c) .NET Foundation. All rights reserved.
 
 			<!-- NOTE: Content is opt-out (must have Pack=false to exclude if IncludeContentInPackage=true) -->
 			<!-- Stuff that is copied to output should be included from that output location -->
-			<_InferredPackageFile Include="@(_ContentToInfer->'$(OutputPath)%(TargetPath)')"
+			<_InferredPackageFile Include="@(_ContentToInfer->'$(_OutputFullPath)\%(TargetPath)')"
 							   Condition="'%(_ContentToInfer.CopyToOutputDirectory)' != '' and '%(_ContentToInfer.CopyToOutputDirectory)' != 'Never'">
 				<Kind Condition="'%(_ContentToInfer.Kind)' == ''">$(PrimaryOutputKind)</Kind>
 			</_InferredPackageFile>
@@ -118,7 +121,7 @@ Copyright (c) .NET Foundation. All rights reserved.
 
 			<!-- NOTE: None is also opt-out (must have Pack=false to exclude if IncludeNoneInPackage=true, but this property defaults to false) -->
 			<!-- Likewise, include from target path if it's copied, from source path otherwise -->
-			<_InferredPackageFile Include="@(_NoneToInfer->'$(OutputPath)%(TargetPath)')"
+			<_InferredPackageFile Include="@(_NoneToInfer->'$(_OutputFullPath)\%(TargetPath)')"
 							   Condition="'%(_NoneToInfer.CopyToOutputDirectory)' != '' and '%(_NoneToInfer.CopyToOutputDirectory)' != 'Never'">
 				<Kind Condition="'%(_NoneToInfer.Kind)' == ''">$(PrimaryOutputKind)</Kind>
 			</_InferredPackageFile>

src/Build/NuGet.Build.Packaging.Tests/given_duplicate_package_files.cs

@@ -53,7 +53,6 @@ public void same_source_different_target_are_preserved()
 			Assert.Equal(TargetResultCode.Success, result.ResultCode);
 		}
 
-
 		[Fact]
 		public void real_duplicates_fail()
 		{