submodule: port subcommand 'set-url' from shell to C

Convert submodule subcommand 'set-url' to a builtin. Port 'set-url' to
'submodule--helper.c' and call the latter via 'git-submodule.sh'.

Signed-off-by: Shourya Shukla <shouryashukla.oo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -805,27 +805,7 @@ cmd_set_url() {
 		shift
 	done
 
-	if test $# -ne 2
-	then
-		usage
-	fi
-
-	# we can't use `git submodule--helper name` here because internally, it
-	# hashes the path so a trailing slash could lead to an unintentional no match
-	name="$(git submodule--helper list "$1" | cut -f2)"
-	if test -z "$name"
-	then
-		exit 1
-	fi
-
-	url="$2"
-	if test -z "$url"
-	then
-		exit 1
-	fi
-
-	git submodule--helper config submodule."$name".url "$url"
-	git submodule--helper sync ${GIT_QUIET:+--quiet} "$name"
+	git ${wt_prefix:+-C "$wt_prefix"} ${prefix:+--super-prefix "$prefix"} submodule--helper set-url ${GIT_QUIET:+--quiet} -- "$@"
 }
 
 #