Platform specific test suite for .NET Framework to run in CI

[daveleek]

Is your feature request related to a problem? Please describe.
We need to make sure our SDK continues to run on both .NET Framework (Windows only) and .NET Core when we add features or fix bugs. Adding a test project that only runs on .NET Framework should be enough. See #204 for context

Describe the solution you'd like
Add a test project with some tests that runs on .NET Framework only.

Describe alternatives you've considered
None

Additional context
None

[sighphyre]

I'd really like to have a test set that runs on every framework we support, ideally

[sighphyre]

Pinned this so our bots don't decide to kill it