[llvm-objcopy][MachO] Implement --redefine-sym and --redefine-syms

Similar to D46029 (ELF) and D70036 (COFF), but for MachO.
Note, when --strip-symbol (not implemented for MachO) is also specified,
--redefine-sym executes before --strip-symbol.

Reviewed By: jhenderson, seiya

Differential Revision: https://reviews.llvm.org/D70212