builtin rebase: add support for custom merge strategies
When running a rebase in non-am mode, it uses the recursive merge to
cherry-pick the commits, and the rebase command allows to configure
the merge strategy to be used in this operation.
This commit adds that support to the builtin rebase.
Signed-off-by: Pratik Karki <predatoramigo@gmail.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>