Fix debug info size statistics for split dwarf (#80218)

`statistics dump` command relies on `SymbolFile::GetDebugInfoSize()` to
get total debug info size.
The current implementation is missing debug info for split dwarf
scenarios which requires getting debug info from separate dwo/dwp files.
This patch fixes this issue for split dwarf by parsing debug info from
dwp/dwo.

New yaml tests are added.

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Co-authored-by: jeffreytan81 <jeffreytan@fb.com>