Merge branch 'ps/history-drop'

The experimental 'git history' command has been taught a new 'drop' subcommand to remove a commit, with its descendants replayed onto its parent. * ps/history-drop: builtin/history: implement "drop" subcommand builtin/history: split handling of ref updates into two phases replay: expose `replay_result_queue_update()` reset: stop assuming that the caller passes in a clean index reset: allow the caller to specify the current HEAD object reset: introduce ability to skip updating HEAD reset: introduce dry-run mode reset: modernize flags passed to `reset_working_tree()` reset: rename `reset_head()` reset: drop `USE_THE_REPOSITORY_VARIABLE` read-cache: split out function to drop unmerged entries to stage 0