Buildcheck template - grace handle names/dirs starting with numbers

### Context

If `msbuildcheck` template is being instantiated with name (or implicit name derived from the current dir name) that starts with number - the include item fro the 'magic' props is broken

### Repro steps

* `dotnet new msbuildcheck -n 123`
* The created csproj will contain broken include (the name `_123.props` doesn't correspond with the filename - `123.props`):
```




```

### Analysis

This has to do with templating feature that is trying to make the names a valid C# token names - so numbers are auto-prefixed with '_'. We need to make sure that the include link is not expanded like this, or that the props file name is generated that way