[Fix] Bugzilla #18235 - System.Runtime.Caching.MemoryCache doesn't order expirable items correctly
- BubbleUp() in MemoryCacheEntryPriorityQueue was not ordering correctly on item insert
- Added a test case
[Fix] Bugzilla #18182 - ConcurrentQueue<T>.TryPeek() is not thread safe
- removed IsEmpty test from TryPeek() since not needed now