doc txt & -h consistency: fix incorrect alternates syntax

Fix the incorrect "[-o | --option <argument>]" syntax, which should be
"[(-o | --option) <argument>]", we were previously claiming that only
the long option accepted the "<argument>", which isn't what we meant.

This syntax issue for "bugreport" originated in
238b439d69 (bugreport: add tool to generate debugging info,
2020-04-16), and for "diagnose" in 6783fd3cef (builtin/diagnose.c:
create 'git diagnose' builtin, 2022-08-12), which copied and adjusted
"bugreport" documentation and code.

In the case of "Documentation/git-stash.txt" and "builtin/stash.c"
this is not a "doc txt & -h consistency" change, as we're changing
both versions, doing so here makes a subsequent change smaller.

In that case fix the incorrect "[-o | --option <argument>]" syntax,
which should be "[(-o | --option) <argument>]", we were previously
claiming that only the long option accepted the "<argument>", which
isn't what we meant.

The "stash" issue has been with us in both the "-h" and *.txt versions
since bd514cada4 (stash: introduce 'git stash store', 2013-06-15).

We could claim that this isn't a syntax issue if a "vertical bar binds
tighter than option and its argument", but such a rule would change
e.g. this "cat-file" SYNOPSIS example to mean something we don't:

	... [<rev>:<path|tree-ish> | --path=<path|tree-ish> <rev>]

We have various other examples where the post-image here is already
used, e.g. for "format-patch" ("-o"), "grep" ("-m"),
"submodule" ("set-branch -b") etc.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/diagnose.c

@@ -3,7 +3,7 @@
 #include "diagnose.h"
 
 static const char * const diagnose_usage[] = {
-	N_("git diagnose [-o|--output-directory <path>] [-s|--suffix <format>]\n"
+	N_("git diagnose [(-o|--output-directory) <path>] [(-s|--suffix) <format>]\n"
 	   "             [--mode=<mode>]"),
 	NULL
 };