[BOLT][DWARF] Add ability to insert new entries in to DIE

Added ability to append new entries to DIE. This is useful to standadize DWARF4
Split Dwarf, and simplify implementation of DWARF5.
Multiple DIEs can share an abbrev. So currently limitation is that only unique
Attributes can be added.

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D119577