[Deprecation] Switch to QXmlStreamReader

[suamor]

Description:
On Ubuntu 24.04 there are a lot of deprecation warnings. Not a problem with Qt5 but since Qt5 will be removed in the near future, we probably need to switch to QXmlStreamReader.

Warnings: (not all listed, but basically all import and export classes using xml)
/home/suamor/projekte/canorus/gh/canorus/src/import/canorusmlimport.h:36:51: warning: 'QXmlDefaultHandler' is deprecated [-Wdeprecated-declarations]
36 | class CACanorusMLImport : public CAImport, public QXmlDefaultHandler {

In file included from /home/suamor/projekte/canorus/gh/build-canorus-Qt5_15_2-Debug/src/canoruspythonPYTHON_wrap.cxx:3983:
/home/suamor/projekte/canorus/gh/canorus/src/import/canorusmlimport.h:50:27: warning: 'QXmlParseException' is deprecated [-Wdeprecated-declarations]
50 | bool fatalError(const QXmlParseException& exception);

In file included from /home/suamor/projekte/canorus/gh/build-canorus-Qt5_15_2-Debug/src/canoruspythonPYTHON_wrap.cxx:4003:
/home/suamor/projekte/canorus/gh/canorus/src/interface/pluginmanager.h:25:32: warning: 'QXmlDefaultHandler' is deprecated [-Wdeprecated-declarations]
25 | class CAPluginManager : public QXmlDefaultHandler

In file included from /home/suamor/projekte/canorus/gh/canorus/src/interface/pluginmanager.cpp:16:
/home/suamor/projekte/canorus/gh/canorus/src/interface/pluginmanager.h:52:27: warning: 'QXmlParseException' is deprecated [-Wdeprecated-declarations]
52 | bool fatalError(const QXmlParseException& exception);

ToDo:
While normally these warnings could just be ignored for now they generate a huge amount of noise so that important warnings get easily overlooked. I'm even thinking of temporarily suppressing deprecation warnings.

DoD:
QXmlStreamReader implemented in all mentioned classes

Alternatively:
Switch to Qt 6.5 (which requires other porting work)