Implement `ReflectionAnalysis::get_class_source`
Implement `ReflectionAnalysis::get_class_source`

Summary: Implemented `ReflectionAnalysis::get_class_source` which already had a definition in `ReflecitonAnalysis.h`. Essentially just a wrapper on `BaseIRAnalyzer<AbstractObjectEnvironment>::get_class_source`

Reviewed By: yuxuanchen1997

Differential Revision: D31658517

fbshipit-source-id: f64b9ce0aaea8e17b850cf52c2ad50b0de6e4a80

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex