Helper type that can be used to get `ICustomKey` for any object (including objects that actually implement the interface and tuples)

Represents a special hierarchical key. This is mainly used in pretty printing (where we want to get parts of the keys based on levels. `CustomKey.Get` provides a way of getting `ICustomKey`.

Implements a simple lookup that matches any multi-level key against a specified array of optional objects (that represent missing/set parts of a key)