WindowsSnapshotProvider should obtain memory value from Environment.WorkingSet only

[evgenyfedorov2]

The GetSnapshot() method of the WindowsSnapshotProvider class currently gets memory usage value using
(ulong)process.WorkingSet64, while the GetMemoryUsageInBytes() method in the same class correctly and more performantly uses Environment.WorkingSet.

Please update GetSnapshot() to use Environment.WorkingSet.