[flang][NFC] Add source line to lowering TODO messages
- Add a fatal error handler that can print a message with source location before aborting.
- Update TODO macro to take an mlir location argument and to use the newly introduced fatal error handler.
- Introduce TODO_NOLOC for the few places where no source location is easily accessible.
Reviewed By: schweitz
Differential Revision: https://reviews.llvm.org/D97190