Merge branch 'sg/parse-options-subcommand'

Introduce the "subcommand" mode to parse-options API and update the
command line parser of Git commands with subcommands.

* sg/parse-options-subcommand: (23 commits)
  remote: run "remote rm" argv through parse_options()
  maintenance: add parse-options boilerplate for subcommands
  pass subcommand "prefix" arguments to parse_options()
  builtin/worktree.c: let parse-options parse subcommands
  builtin/stash.c: let parse-options parse subcommands
  builtin/sparse-checkout.c: let parse-options parse subcommands
  builtin/remote.c: let parse-options parse subcommands
  builtin/reflog.c: let parse-options parse subcommands
  builtin/notes.c: let parse-options parse subcommands
  builtin/multi-pack-index.c: let parse-options parse subcommands
  builtin/hook.c: let parse-options parse subcommands
  builtin/gc.c: let parse-options parse 'git maintenance's subcommands
  builtin/commit-graph.c: let parse-options parse subcommands
  builtin/bundle.c: let parse-options parse subcommands
  parse-options: add support for parsing subcommands
  parse-options: drop leading space from '--git-completion-helper' output
  parse-options: clarify the limitations of PARSE_OPT_NODASH
  parse-options: PARSE_OPT_KEEP_UNKNOWN only applies to --options
  api-parse-options.txt: fix description of OPT_CMDMODE
  t0040-parse-options: test parse_options() with various 'parse_opt_flags'
  ...

t/t5318-commit-graph.sh

@@ -12,12 +12,12 @@ test_expect_success 'usage' '
 
 test_expect_success 'usage shown without sub-command' '
 	test_expect_code 129 git commit-graph 2>err &&
-	! grep error: err
+	grep usage: err
 '
 
 test_expect_success 'usage shown with an error on unknown sub-command' '
 	cat >expect <<-\EOF &&
-	error: unrecognized subcommand: unknown
+	error: unknown subcommand: `unknown'\''
 	EOF
 	test_expect_code 129 git commit-graph unknown 2>stderr &&
 	grep error stderr >actual &&