[5.x] Restore nav/structure select behavior

[JohnathonKoster]

This PR restores the functionality of the nav tag's select parameter. The BulkAugmentor did not know how to resolve those; this PR adds the ability to specify a custom callback that will be used to retrieve augmentation keys. When present, the bulk augmentor will utilize this. If the callback returns null, it will default to its original behavior.

The nav tag uses its getQuerySelectKeys method as its callback to avoid copying that logic into the BulkAugmentor