Shared Mutex Improvement

I improved `MutexMultiProcessFileAppender` to enable the mutex to be shared among all processes and sessions.

The original implementation created a mutex with a default security descriptor (the primary or impersonation token of the creator), which prevented it from being shared between e.g. IIS application pools with different identities. It also didn't use the global kernel object namespace, preventing the mutex from being shared between processes in different sessions.