.NET: Add support for SyncAsyncEventHandlerExtensions.RaiseAsync to async analyzer

See https://github.com/Azure/azure-sdk-for-net/pull/18170 until SyncAsyncEventHandler is merged into Azure.Core.

`SyncAsyncEventHandlerExtensions.RaiseAsync` doesn't take `bool async` and `CancellationToken cancellationToken` parameters because they're already being passed in the `SyncAsyncEventArgs`. We should update the analyzer to verify this as part of the pattern. This is a lower priority because we will not have very many `SyncAsyncEventHandler`s.

Start with the async analyzer entry point that handles SyncAsyncEventHandler patterns and read the referenced Azure SDK pull request for the SyncAsyncEventHandler design. Verify how SyncAsyncEventHandlerExtensions.RaiseAsync is recognized when async and cancellationToken are carried by SyncAsyncEventArgs, and update the analyzer's validation accordingly.

Written by the indexing model from the issue text.