[llvm-lib] [llvm-readobj] [llvm-cvtres] Add Support for ARM64X object files.

Similar to D125411, but for ARM64X.

ARM64X PE binaries are hybrids containing both ARM64EC and pure ARM64
variants in one file. They are usually linked by passing separate
ARM64EC and ARM64 object files to linker. Linked binaries use ARM64
machine and contain additional CHPE metadata in their load config.
CHPE metadata support is not part of this patch, I plan to send that later.

Using ARM64X as a machine type of object files themselves is somewhat
ambiguous, but such files are allowed by MSVC. It treats them as ARM64
or ARM64EC object, depending on the context. Such objects can be
produced with cvtres.exe -machine:arm64x.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D148517