javascript: Support '%m$' in format strings

javascript: Support '%m$' in format strings

Gjs has had support for numbered arguments in format strings since 1.40.
Recognize it as well in format-javascript, so msgfmt -c doesn't fail
when numbered arguments are in msgstr.  Reported by Sean Burke in:
https://lists.gnu.org/archive/html/bug-gettext/2015-10/msg00002.html
* gettext-tools/src/format-javascript.c (struct numbered_arg): New
struct.
(struct spec): Rename format_args_count to numbered_arg_count.  Add
NUMBERED field in place of FORMAT_ARGS.  All callers changed.
(numbered_arg_compare): New function.
(format_parse): Handle numbered arguments.  Based on format-awk.c.
(format_check): Add check for numbered arguments.
* gettext-tools/tests/format-javascript-1: Add tests for numbered
arguments.
* gettext-tools/tests/lang-javascript: Use numbered argument in format
strings.  Add check for Gjs version >= 1.40.