Fix support for libxml2-2.12 with its api and header changes

[parona-source]

https://gitlab.gnome.org/GNOME/libxml2/-/commit/45470611b047db78106dcb2fdbd4164163c15ab7

In file included from /var/tmp/portage/dev-db/mysql-workbench-8.0.36/work/mysql-workbench-community-8.0.36-src/tools/genobj/genobj.cpp:32:
/var/tmp/portage/dev-db/mysql-workbench-8.0.36/work/mysql-workbench-community-8.0.36-src/library/grt/src/grt.h:2115:59: error: ‘xmlNodePtr’ has not been declared
 2115 |     static MetaClass *from_xml(const std::string &source, xmlNodePtr node);
      |                                                           ^~~~~~~~~~
/var/tmp/portage/dev-db/mysql-workbench-8.0.36/work/mysql-workbench-community-8.0.36-src/library/grt/src/grt.h:2153:19: error: ‘xmlNodePtr’ has not been declared
 2153 |     void load_xml(xmlNodePtr node);
      |                   ^~~~~~~~~~
/var/tmp/portage/dev-db/mysql-workbench-8.0.36/work/mysql-workbench-community-8.0.36-src/library/grt/src/grt.h:2154:30: error: ‘xmlNodePtr’ has not been declared
 2154 |     void load_attribute_list(xmlNodePtr node, const std::string &member = "");
      |                              ^~~~~~~~~~
/var/tmp/portage/dev-db/mysql-workbench-8.0.36/work/mysql-workbench-community-8.0.36-src/library/grt/src/grt.h:2534:5: error: ‘xmlDocPtr’ does not name a type
 2534 |     xmlDocPtr load_xml(const std::string &path);
      |     ^~~~~~~~~
/var/tmp/portage/dev-db/mysql-workbench-8.0.36/work/mysql-workbench-community-8.0.36-src/library/grt/src/grt.h:2535:27: error: ‘xmlDocPtr’ has not been declared
 2535 |     void get_xml_metainfo(xmlDocPtr doc, std::string &doctype_ret, std::string &version_ret);
      |                           ^~~~~~~~~
/var/tmp/portage/dev-db/mysql-workbench-8.0.36/work/mysql-workbench-community-8.0.36-src/library/grt/src/grt.h:2536:30: error: ‘xmlDocPtr’ has not been declared
 2536 |     ValueRef unserialize_xml(xmlDocPtr doc, const std::string &source_path);

[mysql-oca-bot]

Hi, thank you for submitting this pull request. In order to consider your code we need you to sign the Oracle Contribution Agreement (OCA). Please review the details and follow the instructions at https://oca.opensource.oracle.com/
Please make sure to include your MySQL bug system user (email) in the returned form.
Thanks

[mysql-oca-bot]

Hi, thank you for your contribution. Please confirm this code is submitted under the terms of the OCA (Oracle's Contribution Agreement) you have previously signed by cutting and pasting the following text as a comment:
"I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it."
Thanks

[parona-source]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

[mysql-oca-bot]

Hi, thank you for your contribution. Your code has been assigned to an internal queue. Please follow
bug http://bugs.mysql.com/bug.php?id=113840 for updates.
Thanks