Fix a small memory leak in libgettextpo.

Fix a small memory leak in libgettextpo.

Reported by <gemmaro.dev@gmail.com> at
<https://savannah.gnu.org/bugs/index.php?item_id=67892>
and by Albert Astals Cid <aacid@kde.org> in
<https://lists.gnu.org/archive/html/bug-gettext/2026-01/msg00071.html>.

* gettext-tools/src/read-po-lex.h: Include str-list.h.
(lex_start): Add arena parameter.
* gettext-tools/src/read-po-lex.c (lex_start): Add arena parameter. Add the
heap-allocated file_name to the arena.
* gettext-tools/src/read-catalog-abstract.h: Include str-list.h.
(struct catalog_input_format): Add arena parameter to parse() method.
(catalog_reader_parse): Add arena parameter.
* gettext-tools/src/read-properties.c (properties_parse): Add arena parameter.
* gettext-tools/src/read-stringtable.c (stringtable_parse): Add arena parameter.
* gettext-tools/src/read-po.c (po_parse): Add arena parameter. Update lex_start
call.
* gettext-tools/src/read-catalog-abstract.c (catalog_reader_parse): Add arena
parameter. Update parse() method call.
* gettext-tools/src/read-catalog.h: Include str-list.h.
(read_catalog_stream): Add arena parameter.
* gettext-tools/src/read-catalog.c (read_catalog_stream): Add arena parameter.
Update catalog_reader_parse call.
* gettext-tools/src/read-catalog-file.c: Include str-list.h.
(read_catalog_file): Update read_catalog_stream call.
* gettext-tools/src/read-csharp.c: Include str-list.h.
(execute_and_read_po_output): Update read_catalog_stream call.
* gettext-tools/src/read-java.c: Include str-list.h.
(execute_and_read_po_output): Update read_catalog_stream call.
* gettext-tools/src/read-resources.c: Include str-list.h.
(execute_and_read_po_output): Update read_catalog_stream call.
* gettext-tools/src/read-tcl.c: Include str-list.h.
(msgdomain_read_tcl): Update read_catalog_stream call.
* gettext-tools/libgettextpo/gettext-po.c: Include str-list.h.
(struct po_file): Add field 'arena'.
(po_file_create): Initialize it.
(po_file_read): Likewise. Update read_catalog_stream call.
(po_file_free): Destroy the arena.
* gettext-tools/src/msgfmt.c (read_catalog_file_msgfmt): Update
catalog_reader_parse call.
* gettext-tools/src/x-po.c: Include str-list.h.
(extract): Update catalog_reader_parse call.
* gettext-tools/src/xgettext.c (read_exclusion_file): Update
catalog_reader_parse call.