These changes fix a few instances of the following type of warning:
error: ‘void QListWidget::setItemSelected(const QListWidgetItem*, bool)’ is deprecated: Use QListWidgetItem::setSelected() instead [-Werror=deprecated-declarations]
as well as similar warnings for setItemHidden() and
setItemExpanded(). These are just warnings now, but it is planned to
remove the methods for Qt 6:
https://bugreports.qt.io/browse/QTBUG-73048
I tested that LyX can still be built against Qt 4.8.7 with this
commit. Indeed, these methods have been deprecated for a while (it
is just that QT_DEPRECATED_WARNINGS was only turned on by default
starting with 5.13.0). See, e.g.,
https://doc.qt.io/archives/qt-4.7/qlistwidget-obsolete.html
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.
