Guard Qt6-only deprecation replacements for Qt5 compatibility

Three deprecated APIs have replacements that only exist in newer Qt6:
- QLocale::nativeCountryName() -> nativeTerritoryName() (Qt 6.2)
- QDomDocument::setContent() overload -> ParseResult (Qt 6.5)
- qt_ntfs_permission_lookup -> QNtfsPermissionCheckGuard RAII (Qt 6.6)
Each is wrapped in QT_VERSION_CHECK so Qt5 keeps the old path. Clears
4 -Wdeprecated-declarations warnings.

sources/ElementsCollection/elementcollectionhandler.cpp

@@ -143,8 +143,12 @@ ElementsLocation ECHSFileToFile::copyElement(ElementsLocation &source, ElementsL
 		//On windows when user drag and drop an element from the common elements collection
 		//to the custom elements collection, the element file stay in read only mode, and so
 		//user can't save the element
+#if QT_VERSION >= QT_VERSION_CHECK(6, 6, 0)
+		QNtfsPermissionCheckGuard ntfs_guard;
+#else
 		extern Q_CORE_EXPORT int qt_ntfs_permission_lookup;
 		qt_ntfs_permission_lookup++;
+#endif
 		QFile file(destination.fileSystemPath() % "/" % new_elmt_name);
 		if (!file.isWritable()) {
 			if (!file.setPermissions(file.permissions() | QFileDevice::WriteUser)) {
@@ -152,7 +156,9 @@ ElementsLocation ECHSFileToFile::copyElement(ElementsLocation &source, ElementsL
 						 << " in ECHSFileToFile::copyElement";
 			}
 		}
+#if QT_VERSION < QT_VERSION_CHECK(6, 6, 0)
 		qt_ntfs_permission_lookup--;
+#endif
 #endif
 		return ElementsLocation (destination.fileSystemPath() % "/" % new_elmt_name);
 	}

sources/cli_export.cpp

@@ -422,6 +422,14 @@ int checkOneElement(const QString &path)
 		return 2;
 	}
 	QDomDocument doc;
+#if QT_VERSION >= QT_VERSION_CHECK(6, 5, 0)
+	if (const auto result = doc.setContent(&file); !result) {
+		file.close();
+		out << "FAIL  " << path << "  (XML error line "
+			<< result.errorLine << ": " << result.errorMessage << ")\n";
+		return 2;
+	}
+#else
 	QString error;
 	int line = 0;
 	if (!doc.setContent(&file, &error, &line)) {
@@ -430,6 +438,7 @@ int checkOneElement(const QString &path)
 			<< line << ": " << error << ")\n";
 		return 2;
 	}
+#endif
 	file.close();
 
 	const QDomElement root = doc.documentElement();

sources/machine_info.cpp

@@ -150,7 +150,11 @@ void MachineInfo::send_info_to_debug()
 	qInfo()<< "";
 	
 	qInfo()<< " OS System language:"<< QLocale::system().name();
+#if QT_VERSION >= QT_VERSION_CHECK(6, 2, 0)
+	qInfo()<< " OS System Native Country Name:"<< QLocale::system().nativeTerritoryName();
+#else
 	qInfo()<< " OS System Native Country Name:"<< QLocale::system().nativeCountryName();
+#endif
 	qInfo()<< " OS System Native Language Name:"<< QLocale::system().nativeLanguageName();	
 	qInfo()<< "";
 	qInfo()<< " System language defined in QET configuration:"<< QString(QETApp::langFromSetting().toLatin1());