po-mode: Prepare for inclusion in GNU ELPA.

po-mode: Prepare for inclusion in GNU ELPA.

Suggested by Stefan Monnier <monnier@iro.umontreal.ca> in
<https://lists.gnu.org/archive/html/bug-gettext/2026-01/msg00086.html>.

* gettext-tools/emacs/po-mode.el: Add meta-information field 'Version:',
required by ELPA. Move meta-information after the copyright and license notice.
(po-mode-version-string): Move definition.
* gettext-tools/emacs/po-compat.el: Move meta-information after the copyright
and license notice. Convert the file to UTF-8 encoding.