add support for identity

[stevenbrix]

This PR add support for object identity via the WinRTObject class.

Since WinRT Object's have to keep a strong ref to their identity, in order for it to remain valid during the lifetime of the object. I re-used the same logic we use for WinRTClass and made it more generic.

When wrapping a swift object. we check if it is a WinRTObject if it is, we store the weak reference on the wrapper. When retrieving the abi object, we check if it has identity. if it does.

Note: this intentionally doesn't require all objects that implement a WinRTInterface to also support the notion of identity. While that is probably a righteous change to eventually have, i went down that route and decided it was slightly too large of a change for now

Testing

Added a couple tests for identity and also added a memory management test to make sure we aren't leaking the WinRTObject

[tristanlabelle]

Closing due to 6 month stale and I can't remove myself from reviewers to stop receiving daily notifications in Slack. @stevenbrix , please reopen as needed.