xfs: refactor log recovery

This series refactors log recovery by moving recovery code for each log
item type into the source code for the rest of that log item type and
using dispatch function pointers to virtualize the interactions.  This
dramatically reduces the amount of code in xfs_log_recover.c and
increases cohesion throughout the log code.

In this second version, we dispense with the extra indirection for log
intent items.  During log recovery pass 2, committing of the recovered
intent and intent-done items is done directly by creating
xlog_recover_item_types for all intent types.  The recovery functions
that do the work are now called directly through the xfs_log_item ops
structure.  Recovery item sorting is less intrusive, and the buffer and
inode recovery code are in separate files now.

The third version has changes for various minor review comments.
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