[DebugInfo] Support to get TU for hash from .debug_types.dwo section in DWARF4. (#161067)
Using the DWP's cu_index/tu_index only loads the DWO units from the
.debug_info.dwo section for hash, which works fine in DWARF5. However,
tu_index points to .debug_types.dwo section in DWARF4, which can cause
the type unit to be lost due to the incorrect loading target. (Related
discussion in
[811b60f](https://github.com/llvm/llvm-project/commit/811b60f0b99dad4b2989d21dde38d49155b0c4f9))
This patch supports to get the type unit for hash from .debug_types.dwo
section in DWARF4.