Code Generation and T4 Text Templates

https://msdn.microsoft.com/en-us/library/bb126445.aspx

Microsoft's Text Template Transformation Toolkit (usually referred to as "T4") is a template based text generation framework included with Visual Studio. 

T4 source files are usually denoted by the file extension ".tt".

 

Where is CodeGenerationTools

http://stackoverflow.com/questions/6323170/where-is-codegenerationtools

That is not class from assembly. It is included class from another template:

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

This files is normally stored in VS installation directory:

%VSINSTALLDIR%\Common7\IDE\Extensions\Microsoft\Entity Framework Tools\Templates\Includes