C++/CLI tests fail on VS 2026 Helix machines - MSB8020 v143 platform toolset not found

## Description

Multiple C++/CLI tests fail on the `windows.amd64.vs2026.pre.scout.open` Helix queue with:

```
error MSB8020: The build tools for Visual Studio 2022 (Platform Toolset = 'v143') cannot be found.
To build using the v143 build tools, please install Visual Studio 2022 build tools.
```

The C++/CLI test asset `.vcxproj` files target the v143 (VS 2022) platform toolset, but the VS 2026 Helix scout images only have v180 installed.

## Affected Tests

- `Microsoft.NET.Build.Tests.SourceLinkTests.Cpp`
- `Microsoft.NET.Build.Tests.GivenThatWeWantToBuildACppCliProject` (all methods)
- `Microsoft.NET.Build.Tests.GivenThatWeWantToBuildACppCliProjectWithTransitiveDeps` (all methods)
- `Microsoft.NET.Pack.Tests.GivenThatWeWantToPackACppCliProject` (all methods)
- `Microsoft.NET.Publish.Tests.GivenThatWeWantToPublishACppCliProject` (all methods)

## Affected Test Assets

- `test/TestAssets/TestProjects/NetCoreCsharpAppReferenceCppCliLib/NETCoreCppCliTest/NETCoreCppCliTest.vcxproj`
- `test/TestAssets/TestProjects/NetCoreCppCliLibWithTransitiveDeps/NETCoreCppCliTest/NETCoreCppCliTest.vcxproj`
- `test/TestAssets/TestProjects/NetCoreCppCliLibWithTransitiveDeps/NETCoreCppCliTestB/NETCoreCppCliTestB.vcxproj`
- `test/TestAssets/TestProjects/NetCoreCppCliLibWithTransitiveDeps/NETCoreCppCliTestC/NETCoreCppCliTestC.vcxproj`

## Build

https://dev.azure.com/dnceng-public/public/_build/results?buildId=1372766
Helix job: `698f4ee1-5121-4424-b30c-db78b1f1c0d9`, work item: `Microsoft.NET.Build.Tests.dll.16`

## Options

- Update the test asset `.vcxproj` files to use a newer platform toolset (v180)
- Request v143 build tools be installed on the VS 2026 Helix scout images