The `Hub` should resolve the SentryClient in a consistent way

[jamescrosswell]

Not introduced in this PR but reading it made me realize and wonder why we have _ownedClient, and use it in some methods (CaptureUserFeedback and CaptureSession but everywhere else we take the client from the (Scope,SentryClient) tuple (which can change with PushScope and BindClient. It's inconsistent.

Originally posted by @bruno-garcia in https://github.com/getsentry/sentry-dotnet/pull/2949#discussion_r1421896401