Add .NET 8 test project for System.Numerics.Tensors (#96641)

* Add .NET 8 test project for System.Numerics.Tensors

* Update src/libraries/System.Numerics.Tensors/tests/Net8Tests/System.Numerics.Tensors.Net8.Tests.csproj

Co-authored-by: Viktor Hofer <viktor.hofer@microsoft.com>

---------

Co-authored-by: Viktor Hofer <viktor.hofer@microsoft.com>

src/libraries/System.Numerics.Tensors/System.Numerics.Tensors.sln

@@ -41,6 +41,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "ref", "tools\ref", "{9482D7
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tools", "tools", "{F9C2AAB1-C7B0-4E43-BB18-4FB16F6E272B}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "System.Numerics.Tensors.Net8.Tests", "tests\Net8Tests\System.Numerics.Tensors.Net8.Tests.csproj", "{46AD9423-D8C3-44BB-A201-1CCCAB4C6DAF}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -99,13 +101,18 @@ Global
 		{57E57290-3A6A-43F8-8764-D4DC8151F89C}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{57E57290-3A6A-43F8-8764-D4DC8151F89C}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{57E57290-3A6A-43F8-8764-D4DC8151F89C}.Release|Any CPU.Build.0 = Release|Any CPU
+		{46AD9423-D8C3-44BB-A201-1CCCAB4C6DAF}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{46AD9423-D8C3-44BB-A201-1CCCAB4C6DAF}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{46AD9423-D8C3-44BB-A201-1CCCAB4C6DAF}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{46AD9423-D8C3-44BB-A201-1CCCAB4C6DAF}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{9F20CEA1-2216-4432-BBBD-F01E05D17F23} = {DE94CA7D-BB10-4865-85A6-6B694631247F}
 		{4AF6A02D-82C8-4898-9EDF-01F107C25061} = {DE94CA7D-BB10-4865-85A6-6B694631247F}
+		{46AD9423-D8C3-44BB-A201-1CCCAB4C6DAF} = {DE94CA7D-BB10-4865-85A6-6B694631247F}
 		{D311ABE4-10A9-4BB1-89CE-6358C55501A8} = {7AC4B2C7-A55C-4C4F-9B02-77F5CBFFF4AB}
 		{21CB448A-3882-4337-B416-D1A3E0BCFFC5} = {7AC4B2C7-A55C-4C4F-9B02-77F5CBFFF4AB}
 		{1578185F-C4FA-4866-936B-E62AAEDD03B7} = {DF0561A1-3AB8-4B51-AFB4-392EE1DD6247}

src/libraries/System.Numerics.Tensors/tests/Net8Tests/System.Numerics.Tensors.Net8.Tests.csproj

@@ -0,0 +1,29 @@
+<!--
+  As of 1/8/2024, the dotnet/runtime infrastructure will run the TensorPrimitives tests on .NET Framework and .NET 9,
+  but it doesn't support validating the .NET 8 build as well, and the code in the .NET 8 and .NET 9 builds are diverging.
+  To ensure it can be tested, this test project simply references the .NET 8 build directly so that the tests can be run
+  separately against that asset (still running on NetCoreAppCurrent but using the net8.0 build of S.N.Tensors.csproj).
+-->
+
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="..\Helpers.cs" />
+    <Compile Include="..\TensorPrimitives.NonGeneric.Single.cs" />
+    <Compile Include="..\TensorPrimitivesTests.cs" />
+    <Compile Include="..\TensorPrimitives.ConvertTo.cs" />
+    <Compile Include="..\TensorPrimitives.Generic.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\System.Numerics.Tensors.csproj" SkipUseReferenceAssembly="true">
+      <SetTargetFramework>TargetFramework=net8.0</SetTargetFramework>
+    </ProjectReference>
+  </ItemGroup>
+
+</Project>