contrib/wix/defines.wxi

testing: switch to inserting deltas

As the comment in the test specifies, this was relying on storage backend
implementation details. We switch to inserting a raw delta, skipping the
regular insert path to ensure we have the desired outcome. This required
implementing support for handling deltas in the revlog testing code.

Differential Revision: https://phab.mercurial-scm.org/D5116

<Include>

  <?if $(var.Platform) = "x64" ?>
    <?define IsX64 = yes ?>
  <?else?>
    <?define IsX64 = no ?>
  <?endif?>

</Include>