While fixing things for Flatpak (which have a path deduplicating some
of the path parts) works there, it breaks locating the debuglink in
other places such as GNOME OS.
This tries both forms, using the long form first and then the short
form second, since Flatpak is likely a subset of everything that needs
to be located.
If we have a path like /app/bin/gnome-builder and the debug prefix is
/app/lib/debug then we don't want to end up with /app/lib/debug/app/bin
as the real data directory is /app/lib/debug/bin.
This often works with /usr because /usr/lib/debug/usr can link back to it's
parent. But we should try to do the right thing instead of relying on that
anyway.
This brings together the two libraries back into one now that the whole
design is pretty well sorted out. They depend on roughly the same libraries
anyway and it's way easier of the single library can both read and write
the capture files (along with bringing in libsysprof-capture symbols in
a single place).
