[LyX/master] Fix theme import function

[Pavel Sanda]

On Mon, Mar 10, 2025 at 10:55:31AM +0100, Pavel Sanda wrote:
> I think it would be better to stick to one only API

That said I greped out of curiosity our sources and we use QFileInfo on
more places than I thought:
src/frontends/qt/GuiApplication.cpp:#include <QFileInfo>
src/frontends/qt/GuiApplication.cpp:                QFileInfo fi(uifiles[i]);
src/frontends/qt/GuiDocument.cpp:                   QString fn = QFileInfo(it.next()).fileName();
src/frontends/qt/GuiLyXFiles.cpp:           QFileInfo const info = QFileInfo(it.key());
src/frontends/qt/GuiPrefs.cpp:#include <QFileInfo>
src/frontends/qt/GuiTabularCreate.cpp:                      QString fn = QFileInfo(it.next()).fileName();
src/support/TempFile.cpp:#include <QFileInfo>
src/support/TempFile.cpp:   QFileInfo tmp_fi(QDir(toqstr(temp_dir.absoluteFilePath())),
src/support/TempFile.cpp:   QFileInfo tmp_fi(QDir(toqstr(package().temp_dir().absoluteFilePath())),
src/support/filetools.cpp:  QFileInfo tmp_fi(QDir(toqstr(tempdir.absFileName())), toqstr(mask));

(And then lots of it in FileName.cpp.)

Do we want that?

Pavel