[clang-sycl-linker][offload] Set TheImageKind based on IsAOTCompileNeeded flag (#180269)
Previously, TheImageKind was set to IMG_None and relied on a runtime
heuristic to determine the correct image type. This commit sets it
explicitly to IMG_Object for AOT-compiled images and IMG_SPIRV for
SPIR-V images based on the IsAOTCompileNeeded flag.
Also it adds test for this change, which required minor changes in
OffloadBinary and OffloadDump.