migration/hmp: Reorg "info migrate" once more

migration/hmp: Reorg "info migrate" once more

Dave suggested the HMP output for "info migrate" can not only leverage the
lines but also better grouping:

  https://lore.kernel.org/r/aC4_-nMc7FwsMf9p@gallifrey

I followed Dave's suggestion, and some more modifications on top:

  - Added all elements into the picture

  - Use size_to_str() and drop most of the units: benefit is more friendly
  to most human eyes, bad side effect is lose of details, but that should
  be corner case per my uses, and one can still leverage the QMP interface
  when necessary.

  - Sub-grouping for "Transfers" ("Channels" and "Page Types").

  - Better indentations

Sample output:

(qemu) info migrate
Status:                 postcopy-active
Time (ms):              total=47317, setup=5, down=8
RAM info:
  Throughput (Mbps):    1342.83
  Sizes:                pagesize=4 KiB, total=4.02 GiB
  Transfers:            transferred=1.41 GiB, remain=2.46 GiB
    Channels:           precopy=15.2 MiB, multifd=0 B, postcopy=1.39 GiB
    Page Types:         normal=367713, zero=41195
  Page Rates (pps):     transfer=40900, dirty=4
  Others:               dirty_syncs=2, postcopy_req=57503

Suggested-by: Dr. David Alan Gilbert <dave@treblig.org>
Tested-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Li Zhijian <lizhijian@fujitsu.com>
Acked-by: Dr. David Alan Gilbert <dave@treblig.org>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Link: https://lore.kernel.org/r/20250613140801.474264-2-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>