Merge PR #24229 into master

* refs/pull/24229/head:
	common: drop BL_BACKWARD_COMPAT in bufferlist.
	osd: OSDMap encoding uses bufferlist::contiguous_filler.
	mds: encode_xattrs() uses buffer::list::contiguous_filler.
	common: introduce contiguous_filler to optimize ENCODE_START.
	common: optimize hole appending in bufferlist.
	common: duplicate an encoding macro to suppress warnings.
	common: drop backward iteration from bufferlist.

Reviewed-by: Gregory Farnum <gfarnum@redhat.com>
Reviewed-by: Josh Durgin <jdurgin@redhat.com>

diff --cc src/common/buffer.cc
Simple merge

diff --cc src/include/buffer.h
Simple merge

diff --cc src/include/denc.h
Simple merge

diff --cc src/include/encoding.h
Simple merge

diff --cc src/mds/CInode.cc
Simple merge

diff --cc src/msg/simple/Pipe.cc
Simple merge

diff --cc src/os/filestore/FileJournal.h
Simple merge

diff --cc src/osd/osd_types.cc
Simple merge

diff --cc src/test/bufferlist.cc
Simple merge