[DebugInfo] Dump values in .debug_pubnames and .debug_pubtypes according to the DWARF format (6/8).

The patch changes dumping of unit_length, debug_info_offset, and
debug_info_length fields in headers in .debug_pubname and
.debug_pubtypes sections so that they are printed as 16-digit hex values
if the contribution is in the DWARF64 format. Dumping of offsets in the
tables is changed in the same way.

Differential Revision: https://reviews.llvm.org/D79997