[DWARFDebugRnglists] Add a callback-based version of the getAbsoluteRanges function

Summary:
The dump() function already accepts a callback. This makes
getAbsoluteRanges do the same. The existing DWARFUnit overload is
implemented on top of the new function.

This enables usage of the debug_rnglists parser from within lldb (which
has it's own dwarf parser).

Reviewers: dblaikie, JDevlieghere, aprantl

Subscribers: hiraditya, probinson, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70952