[llvm] [llvm-readobj][COFF] Add `--coff-output-style` flag (PR #95074)

[Miguel A. Arroyo via llvm-commits]

mayanez wrote:

>  If an object file is not COFF, report an error. 

That seems reasonable. I'll follow your suggestion.

> If the object file is COFF but requests a JSON-unimplemented dump option, report an error.

I implemented all the options so we shouldn't have to be concerned about this case.

> In separate discussions, we determine what we will do with ELF, perhaps maintain an allow list for ELF as well. This effort is orthogonal to COFF.

Makes sense. 👍 

https://github.com/llvm/llvm-project/pull/95074