Show node IDs in XHPAST tree view

Summary: Currently we do not show node IDs in this view, but do show token IDs in the stream view. Given that this view facilitates testing various XHPAST functionality, it would be useful to add this information.

Test Plan: Saw node IDs in XHPAST.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14697