[OffloadPackager] Add option to extract files from images

We use the `clang-offload-packager` too bundle many files into a single
binary format containing metadata. This is used for offloading
compilation which may contain multiple device binaries of different
types and architectures in a single file. We use this special binary
format to store these files along with some necessary metadata around
them. We use this format because of the difficulty of determining the
filesize of the various binary inputs that will be passed to the
offloading toolchain rather than engineering a solution for each input.

Previously we only support packaing many files into a single binary.
This patch adds support for doing the reverse by using the same
`--image=` syntax. To unpackage a binary we now present an input file
instead of an output.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D129507