msgfmt: New option --replace-text.

msgfmt: New option --replace-text.

Reported by Asterix <asterix@lagaule.org>
at <https://savannah.gnu.org/bugs/?52159>.

* gettext-tools/src/its.h (its_merge_context_merge): Add parameter replace_text.
* gettext-tools/src/its.c (its_merge_context_merge_node): Add parameter
replace_text.
(its_merge_context_merge): Likewise.
* gettext-tools/src/write-xml.h (msgdomain_write_xml, msgdomain_write_xml_bulk):
Add parameter replace_text.
* gettext-tools/src/write-xml.c (msgdomain_write_xml_bulk): Add parameter
replace_text.
(msgdomain_write_xml): Likewise.
* gettext-tools/src/msgfmt.c (xml_replace_text): New variable.
(long_options): Add --replace-text.
(main): Handle --replace-text.
(usage): Document option --replace-text.
* gettext-tools/tests/msgfmt-xml-4: New file, based on
gettext-tools/tests/msgfmt-xml-1.
* gettext-tools/tests/Makefile.am (TESTS): Add it.
* gettext-tools/doc/msgfmt.texi: Document option --replace-text.
* NEWS: Mention the change.