XFS fixes for 4.19-rc6

Accumlated regression and bug fixes for 4.19-rc6, including:

o make iomap correctly mark dirty pages for sub-page block sizes
o fix regression in handling extent-to-btree format conversion errors
o fix torn log wrap detection for new logs
o various corrupt inode detection fixes
o various delalloc state fixes
o cleanup all the missed transaction cancel cases missed from changes merged
  in 4.19-rc1
o fix lockdep false positive on transaction allocation
o fix locking and reference counting on buffer log items
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