Where are types used in Entity Framework T4 templates defined?

Entity Framework T4 template has include directive at the top of the file. For C# it will look like:

<#@ include file="EF6.Utility.CS.ttinclude"#>

This file can be found in Visual Studio IDE extensions folder. E.g. by default for Visual Studio 2017 it will be:

c:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\Extensions\Microsoft\Entity Framework Tools\Templates\Includes\

This file contains helper classes which are used for entities generation. E.g.

/// <summary>
/// Responsible for encapsulating the retrieval and translation of the CodeGeneration
/// annotations in the EntityFramework Metadata to form that is useful in code generation.
/// </summary>
public static class Accessibility

Second class TypeMapper is defined in the context generation template itself.