[DebugInfo]: Refactored Macinfo section consumption part to allow future

[DebugInfo]: Refactored Macinfo section consumption part to allow future
macro section dumping.

Summary: Previously macinfo infrastructure was using functions
names that were ambiguous i.e `getMacro/getMacroDWO` in a sense
of conveying stated intentions. This patch refactored them into more
reasonable `getDebugMacinfo/getDebugMacinfoDWO` names thus making
room for macro implementation.

Reviewers: aprantl, probinson, jini.susan.george, dblaikie

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D75037