Merge branch 'lc/rebase-trailer'

"git rebase" learns "--trailer" command to drive the
interpret-trailers machinery.

* lc/rebase-trailer:
  rebase: support --trailer
  commit, tag: parse --trailer with OPT_STRVEC
  trailer: append trailers without fork/exec
  trailer: libify a couple of functions
  interpret-trailers: refactor create_in_place_tempfile()
  interpret-trailers: factor trailer rewriting

diff --cc builtin/commit.c
Simple merge

diff --cc builtin/rebase.c
Simple merge

diff --cc sequencer.c
Simple merge

diff --cc t/meson.build
Simple merge