Reland "[llvm-readobj][MachO] Add option to sort the symbol table before...

Reland  "[llvm-readobj][MachO] Add option to sort the symbol table before dumping (MachO only, for now)."
    https://reviews.llvm.org/D116787

This reverts commit 33b3c86a.

New change: fixed build failures:
 - in stabs-sorted:restore the the ERR-KEY statements, which were accidentally deleted during refactoring
 - in ObjDumper.h/MachODumper.cpp: refactor so that current dumpers which didn't provide an impl that accept a SymCom still works