.NET Core WPF project template is not available in Blend's New Project dialog

[debonte]

Repro:

1. Install .NET Core 3.0 SDK
2. Start Blend 2019
3. Press the "Create new project..." hyperlink

Expected: "WPF App (.NET Core)" template appears under the Installed\Visual C#\.NET Core node in the template tree.

Actual: There is no .NET Core node under Installed\Visual C#, and the "WPF App (.NET Core)" isn't found anywhere else.

[jmarolf]

As I mentioned on the PR. Blend needs to be resilient to the case where these templates are installed but there is no .NET Core SDK and not show these templates in that situation