Look up synthesized ancestors lazily
Summary:
Replace the use of tc_req_ancestors_extends (the set of names of all require-extends and require-implements ancestors, plus the names of all classes they extend, traits they use, and XHP classes whose attributes they include) when shallow_class_decl is enabled using the linearization.
To do this, we need only collect the names of all ancestors marked with the mro_synthesized flag in the linearization.
Reviewed By: vassilmladenov
Differential Revision:
D14631449
fbshipit-source-id:
3c914fec54fe08cc1ae57b08fc40729406d6dd4d