Change Feed Processor: Fixes disposal of unused CancellationTokenSource

[ealsur]

Once a lease is finished processing, due to split or merge happening or any of the known conditions:

azure-cosmos-dotnet-v3/Microsoft.Azure.Cosmos/src/ChangeFeedProcessor/FeedManagement/PartitionSupervisorCore.cs

Lines 52 to 80 in ea269c9

	catch (LeaseLostException)
	{
	closeReason = ChangeFeedObserverCloseReason.LeaseLost;
	throw;
	}
	catch (FeedRangeGoneException)
	{
	closeReason = ChangeFeedObserverCloseReason.LeaseGone;
	throw;
	}
	catch (CosmosException)
	{
	closeReason = ChangeFeedObserverCloseReason.CosmosException;
	throw;
	}
	catch (OperationCanceledException) when (shutdownToken.IsCancellationRequested)
	{
	closeReason = ChangeFeedObserverCloseReason.Shutdown;
	}
	catch (ChangeFeedProcessorUserException)
	{
	closeReason = ChangeFeedObserverCloseReason.ObserverError;
	throw;
	}
	catch (Exception) when (processorTask.IsFaulted)
	{
	closeReason = ChangeFeedObserverCloseReason.Unknown;
	throw;
	}

The PartitionSupervisor variable is no longer used and goes out of scope to be GCed.

The PartitionSupervisor implements IDisposable but there is no path that explicitly calls Dispose when the supervisor is no longer used.

Closes #4208

[FabianMeiswinkel]

LGTM