* lang_php/parsing/parser_php.mly: comments
pfff: support @ soft type annotation

Test Plan: unit test included

Reviewers: amenghra, pieter, glevi, jiaol, ashwin

Reviewed By: ashwin

CC: ashwin

Differential Revision: https://phabricator.fb.com/D902460

Task ID: 2630429
* lang_php/analyze/foundation/graph_code_php.ml: comment
* tests/php/codegraph/xhp_use.php:
* lang_php/analyze/foundation/graph_code_php.ml: better error on undefined
class constants that are actually undefined class
* h_program-lang/graph_code.ml: misc
* lang_php/analyze/foundation/graph_code_php.ml: fix comment
* lang_php/analyze/foundation/graph_code_php.mli: clean
* lang_php/analyze/foundation/graph_code_php.ml: estet
* tests/php/codegraph/pfff_test.exp: adjust
* lang_php/analyze/foundation/graph_code_php.ml: