[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