Enable gradual migration of FFP errors away from CST
Summary:
Now that error reporting in lowering is decoupled from building AST
(by capturing side effects and replaying them via flush_parsing_errors),
reuse the same mechanism for prioritizing syntax errors emitted
from the Full_fidelity_syntax_errors module but also merge them
with errors from a *new* phase of error checking on lowered AST.
This way, existing error checks can be *gradually* moved from CST to AST
or to the parser itself (for those which cannot be detected after lowering).
Reviewed By: oulgen
Differential Revision:
D13985463
fbshipit-source-id:
3f28889e6a6a4d8011d8dc24bab167d44f20d5a4