getRelocationValueString is a dispatcher function that calls the
corresponding ELF/COFF/Wasm/MachO implementations
that currently live in the llvm-objdump.cpp file.
I think these implementations should be moved to ELFDump.cpp,
COFFDump.cpp and other corresponding files, to move platform specific
implementation out from the common logic.
The patch does that. Also, I had to move ToolSectionFilter helper and SectionFilterIterator,
SectionFilter to a header to make them available across the objdump code.
That was needed for COFF, other implementations do not use ToolSectionFilter.
But it should be OK.
It depends on D56721 that was LGTMed but not yet landed.