scripts/analyze-migration: Support mapped-ram snapshot format

scripts/analyze-migration: Support mapped-ram snapshot format

The script has not been updated to read mapped-ram snapshots and is currently
crashing when trying to read such a file.

With this commit, it can now read a snapshot created with:

    (qemu) migrate_set_capability x-ignore-shared on
    (qemu) migrate_set_capability mapped-ram on
    (qemu) migrate -d file:vm.state

Signed-off-by: Pawel Zmarzly <pzmarzly0@gmail.com>
Link: https://lore.kernel.org/r/20251126155015.941129-1-pzmarzly0@gmail.com
[peterx: space fixes, introduce parseMappedRamBlob(), add comments, etc.]
Signed-off-by: Peter Xu <peterx@redhat.com>