An attempt at class attr refs

[keyz182]

Draft because I'm struggling to get debugging and building working on Fedora, so I've not actually run/tested the code.

This is an attempt to have go-to references on Class="foo" attributes, e.g. WorldGenStep_Lakes in:

  <WorldGenStepDef>
    <defName>Lakes</defName>
    <order>150</order>
    <worldGenStep Class="WorldGenStep_Lakes"/>
  </WorldGenStepDef>