Add developer-oriented documentation to GetDeferral

[fvanheeswijk]

Currently the GetDeferral and CoreWebView2Deferral documentation is not developer-friendly, the latter has the following documentation:

• Complete(): Completes the associated deferred event.
• Dispose(): Public implementation of Dispose pattern.
• Dispose(Boolean): Protected implementation of Dispose pattern.

However Threading model for WebView2 apps > Deferrals > Deferrals in C# indicates that Complete() should not be called but using should be used and thus Dispose() should be called. I think the documentation should be updated to reflect that.

AB#40463981

[nishitha-burman]

Thanks for the feedback! We've added this as a scenario on our backlog!

[obartelt]

It should also be added that calling Dispose after calling Complete leads to a COMException. Ran into that today, should probably be fixed (or the documentation updated).