In modern podman, we will get lowerdir= and upperdir= in the superblock
options which we can parse to find where things are on the host. Use that
instead of relying on overlay mounts.
Additionally, if we're on a subvolume, and that subvolume matches the
prefix of the root, then skip past that. I have no idea if this is the
right thing to do, but it's what we were doing before and seems to be
able to help us get proper path resolving on Silverblue.
I highly doubt this is foolproof, but this makes Silverblue more likely to
resolve the proper fstab entry when translating to paths we can access
from the host system.
And expose it via sysprof_document_process_list_mounts() so that when
inspecting processes we can see what binaries were mapped as well as what
the filesystem looked like to locate those mapped paths.
The goal here is that we can try to reproduce to some degree the mount
namespace as the PID saw it, but also convert that to paths where we can
find the files on the host system.
