This revision implement new mechanism for DWARFRewriter.
In the new mechanism, we adopt the same way with DWARFLinker did. By parsing Debug information into IR, we are allowed to handle debug information more flexible. Now the debug information updating process relies on IR and IR will be written out to binary once the updating finished.
A new class was added: DIEBuilder. This class is responsible for parsing debug information and raising it to the IR level.
This class is also used to write out the .debug_info and .debug_abbrev sections.
Since we output brand new Abbrev section we won't need to always convert low_pc/high_pc into ranges.
When conversion does happen we can also remove low_pc entry.