[lldb] Update the String table offset based on the DWARF format (#147054)
This PR is updating the string table offset (DW_AT_str_offsets_base
which is introduced in `DWARF5`) based on the DWARF format, as per the
DWARF specification; For the 32-bit DWARF format, each offset is 4 bytes
long; for the 64-bit DWARF format, each offset is 8 bytes long.