Task: Apply Dictionary<TKey, TValue>, SortedDictionary<TKey, TValue> and SortedSet<T> Breaking API Changes

[NightOwl888]

This is a reminder to revert #113 when we have the next major version bump.

Several of our collections have APIs that use interfaces instead of concrete types for GetEnumerator(), Keys, Values and other members of collection interfaces. These are supposed to return concrete types. In the case of GetEnumerator() it will prevent boxing the Enumerator struct to an interface when the interface on the publicly declared method (the default when used in a foreach loop).