Make XHPAST unit test "expect" blocks stable and human-readable

Summary:
Depends on D21064. Ref T13492. Earlier, see D17819. This is essentially the same change, although I inlined the token stream into the node list.

This intentionally breaks most tests since it just has the new "expect" generator; the next change will fix them by swapping the test bodies.

Test Plan: Ran "arc unit --everything" after the next change (which fixes all the tests), got a clean build. This change on its own fails all existing XHPAST tests since the block formats don't match.

Maniphest Tasks: T13492

Differential Revision: https://secure.phabricator.com/D21065