Fixing multiple type definition issue and fixing NotifyCollectionChangedAction issue

[manodasanW]

• The WebView package and the WinAppSDK 1.5 package both can be referenced by someone and have the same types defined in both. One is an RCW generated by CsWinRT while the other is not as it is for netcore3. Our RCW fallback generator tries to make the WinAppSDK version of it trimming safe but given it is defined in multiple places that leads to a compiler error. It would also be a compiler error already if the component itself tried to use that type. So instead of letting them become a compiler error, we just emit a warning / info to call out we weren't able to make it trim safe and the user should update versions if they need that.
• NotifyCollectionChangedAction wasn't marked as blittable when it should have been as seen in Error CS0122: 'NotifyCollectionChangedAction' is inaccessible due to its protection level #1813