Update to v5.1

Highlights from upstream

• check:
  • repair: flush/FUA support to avoid breaking metadata COW
  • file extents repair no longer relies on data in extent tree
  • lowmem: fix false error reports about gaps between extents
  • add inode mode check and repair for various objects
  • add check for invalid combination of nocow/compressed extents
• device scan: new option to forget scanned devices
• mkfs: use same chunk size as kernel for initial creation
• dev-replace: better report when other exclusive operation is running
• help: for syntax errors on command line, print only the relevant messages, not the whole help text
• receive:
  • new option for quiet mode
  • on -vv print information about written ranges
  • fix endless loop with --dump on an invalid stream
• defrag: able open files in RO mode (needs kernel support to work)
• dump-tree: --block can be specified multiple times
• libbtrfsutil: fix: don't close fd on error in btrfs_util_subvolume_id_fd
• core:
  • add sync before superblock write
  • better error handling on the transaction commit path
  • try to find best copy when reading tree blocks
  • update backup roots on commit transaction
• other:
  • fuzz tests pass and are enabled in CI
  • cleanups
  • new tests