[hack] Identify class names in xhp attribute lists
[hack] Identify class names in xhp attribute lists

Summary:We don't look at them in typing phase, so hooks approach doesn't work, but they can be recovered from NAST.

The worse case are xhp children lists:

```
class :xhp:bar-component {
  children (:xhp:foo-element);
}
```

The entire "children" line is discarded at parsing phase, as evidenced by this function not returning any value:

diffusion/FBS/browse/master/fbcode/hphp/hack/src/parsing/parser_hack.ml;6b3e06b3126005f5ba4b3bce58a8168acf0f6dd5$1360-1383

I'll see what we can do about it.

Reviewed By: int3

Differential Revision: D3209383

fb-gh-sync-id: d2e9291f0deb92e4cfbd0715e6f250a051d0f92b
fbshipit-source-id: d2e9291f0deb92e4cfbd0715e6f250a051d0f92b

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