Add solution explorer goldbar when targeting out-of-support

## Summary
Today we emit out-of-support warnings to the build outputs when targeting out-of-support framework versions:

```
Severity Code Description Project File Line Suppression State
Warning NETSDK1138 The target framework 'net5.0' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy. ConsoleApp144 C:\Program Files\dotnet\sdk\8.0.100\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.EolTargetFrameworks.targets 32
```

We do not put this more boldly in the IDE experience until then. We should consider adding a solution-explorer goldbar to show the same warning:

## User Impact
More direct feedback about targeting out of support frameworks.