Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r256610:
Add unmapped I/O support to GEOM RAID.

MFC r248720:
Remove extra bio_data and bio_length copying to child request after calling
g_clone_bio(), that already copied them.

MFC r242323, r242328:
Add basic BIO_DELETE support to GEOM RAID class for all RAID levels.

If at least one subdisk in the volume supports it, BIO_DELETE requests
will be propagated down. Unfortunatelly, for RAID levels with redundancy
unmapped blocks will be mapped back during first rebuild/resync process.

MFC r240465:
Add global and per-module sysctls/tunables to enable/disable metadata taste.
That should help to handle some cases when disk has some RAID metadata that
should be ignored, especially during boot.

MFC r234458, r234603, r234610, r234727, r234816, r234848, r234868,
r234869, r234899, r234940, r234993, r234994, r235071 -c r235076, r235080,
r235096:
- Add support for the DDF metadata format, as defined by the SNIA Common
RAID Disk Data Format Specification v2.0;
- Add support for reading non-degraded RAID4/5/5E/5EE/5R/6/MDF volumes.

Sponsored by: iXsystems, Inc.

MFC r235270:
- Prevent error status leak if write to some of the RAID1/1E volume disks
failed while write to some other succeeded. Instead mark disk as failed.
- Make RAID1E less aggressive in failing disks to avoid volume breakage.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Bunch of small bugfixes and cleanups.

Found with: Clang Static Analyzer

MFgraid/head:
Add new RAID GEOM class, that is going to replace ataraid(4) in supporting
various BIOS-based software RAIDs. Unlike ataraid(4) this implementation
does not depend on legacy ata(4) subsystem and can be used with any disk
drivers, including new CAM-based ones (ahci(4), siis(4), mvs(4), ata(4)
with `options ATA_CAM`). To make code more readable and extensible, this
implementation follows modular design, including core part and two sets
of modules, implementing support for different metadata formats and RAID
levels.

Support for such popular metadata formats is now implemented:
Intel, JMicron, NVIDIA, Promise (also used by AMD/ATI) and SiliconImage.

Such RAID levels are now supported:
RAID0, RAID1, RAID1E, RAID10, SINGLE, CONCAT.

For any all of these RAID levels and metadata formats this class supports
full cycle of volume operations: reading, writing, creation, deletion,
disk removal and insertion, rebuilding, dirty shutdown detection
and resynchronization, bad sector recovery, faulty disks tracking,
hot-spare disks. For Intel and Promise formats there is support multiple
volumes per disk set.

Look graid(8) manual page for additional details.

Co-authored by: imp
Sponsored by: Cisco Systems, Inc. and iXsystems, Inc.