Extend `DebugInfoFinder` to collect and expose macro debug information
(`DIMacro` and `DIMacroFile` nodes).
Also update `ModuleDebugInfoPrinter` to display macro information
including the macro type, name, value, and source location.
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The motivation behind this PR is that `DebugInfoFinder` is key for the
[SPIRV-LLVM-Translator](https://github.com/KhronosGroup/SPIRV-LLVM-Translator)
and also for future support of debug info in the SPIRV backend in LLVM.
This new lookup of `DIMacro` with their `DIMacroFile` when available
simplifies the logic around the translation for this debug information.
c8d8e5e210