These extension methods exist for CQLinq friendly syntax reasons and can only be called in a ICQLinqExecutionContext.
Indeed they all require a special resolving step prior to query execution, that resolves once for all code elements by name.
The user doesn't have to write this resolving code. This results in less syntax burden.
For each of these extension methods, there are one or several corresponding methods in NDepend.CodeModel, that can be called to get the same action done.
This pre-resolving step is weaved at CQLinq compilation time, the CQLinq compiler takes care of transforming calls to these extension methods to calls to their NDepend.CodeModel equivalent.
These extension methods cannot be called from a program consuming NDepend.API, since it would provoke the resolving step to be invoked for all code elements.

Reference

ExtensionMethodsCQLinqDependency Members
NDepend.Reserved.CQLinq Namespace