PR30809: improve debuginfod client progress-callback parameters

PR30809: improve debuginfod client progress-callback parameters

* debuginfod-client.c (debuginfod_query_server): Use fstat(3)
  of the file handle being downloaded into as the preferred
  source of download progress.

Tested by hand, as the testsuite doesn't have enough machinery to
simulate compressed vs. uncompressed service.  Hand testing with
(unmodified) fedora-38 gdb and debuginfod-find shows dramatically
improved progress displays: all have quantitative figures when
fetching from real (unmodified) upstream servers.

Signed-off-by: Frank Ch. Eigler <fche@redhat.com>