Improve test coverage

[ujjwalchadha]

The current test coverage of CsWinRt seems to exclude some important scenarios. There's a need for a robust testing plan and test cases that can cover most of the APIs. I see the following scenarios at the moment for testing:

1. Test the generated projections for Windows SDK (Not sure if it's possible to test all the APIs manually. We might be able to come up with some automated tests).
2. Test generated projections for WinUI. (There's a need to figure out how to test the XAML types. Also might need automated tests here).
3. Test manual type mappings WinRt.Runtime/Projections
4. Test other required files in WinRt.Runtime
5. Test components in cswinrt/strings/additions

We might be able to do 2 types of testing here:

1. Calling the API methods and properties to check for NullReferenceException, InvalidCastExceptions etc: These types of tests might be automated. And we can test a lot more APIs as there is no logic check required.

2. Checking if the APIs give the expected output: These tests will require individual manual tests. We can test some but not all the APIs.

List of focus areas:

• [x] Manual Type Mappings
• [x] Derived/Composable types #463
• [x] WinUI IReferenceTracker validation
• [ ] #1061
• [x] #778
• [x] Enable x86 testing #341
• [ ] #1060

[ujjwalchadha]

@Scottj1s FYI