Convert projects to use FrameworkReference

[TimothyMothra]

Fix Issue #2251

This affects test projects.
Our SDKs target NetStandard2.0, but our Test projects target individual frameworks.

Changes

• convert test projects to use FrameworkReference

Checklist

• I ran Unit Tests locally.
• CHANGELOG.md updated with one line description of the fix, and a link to the original issue if available.

For significant contributions please make sure you have completed the following items:

• Design discussion issue #
• Changes in public surface reviewed

The PR will trigger build, unit tests, and functional tests automatically. Please follow these instructions to build and test locally.

Notes for authors:

• FxCop and other analyzers will fail the build. To see these errors yourself, compile localy using the Release configuration.

Notes for reviewers:

• We support comment build triggers
  • /AzurePipelines run will queue all builds
  • /AzurePipelines run <pipeline-name> will queue a specific build

[rajkumar-rangaraj]

This is correct. By default all ASP.NET Core 2.1 app had IHostingEnvironment reference in startup.cs. As we are retiring .NET Core 2.1 we need to move from IHostingEnvironment to IWebHostEnvironment. This change is not simple, it requires modification to DefaultApplicationInsightsServiceConfigureOptions.cs. This is out of the scope for this PR.