Merge branch 'nd/switch-and-restore'

Two new commands "git switch" and "git restore" are introduced to
split "checking out a branch to work on advancing its history" and
"checking out paths out of the index and/or a tree-ish to work on
advancing the current history" out of the single "git checkout"
command.

* nd/switch-and-restore: (46 commits)
  completion: disable dwim on "git switch -d"
  switch: allow to switch in the middle of bisect
  t2027: use test_must_be_empty
  Declare both git-switch and git-restore experimental
  help: move git-diff and git-reset to different groups
  doc: promote "git restore"
  user-manual.txt: prefer 'merge --abort' over 'reset --hard'
  completion: support restore
  t: add tests for restore
  restore: support --patch
  restore: replace --force with --ignore-unmerged
  restore: default to --source=HEAD when only --staged is specified
  restore: reject invalid combinations with --staged
  restore: add --worktree and --staged
  checkout: factor out worktree checkout code
  restore: disable overlay mode by default
  restore: make pathspec mandatory
  restore: take tree-ish from --source option instead
  checkout: split part of it to new command 'restore'
  doc: promote "git switch"
  ...

builtin/reset.c

@@ -421,7 +421,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 			print_new_head_line(lookup_commit_reference(the_repository, &oid));
 	}
 	if (!pathspec.nr)
-		remove_branch_state(the_repository);
+		remove_branch_state(the_repository, 0);
 
 	return update_ref_status;
 }