We will not do a copy+delete if the destination is on another mount
point (in fact, QFile uses QTemporaryFile for the latter). In my
opinion, that's a misfeature in QFile, because such an operation may
need to display a progress bar to the user so they won't think the
application has frozen. But it's too late to change now.
I don't know why QTemporaryFile is different. It might be because it was
used for the atomic materialization of a file before QSaveFile existed
(5.1) but I didn't research to confirm. It's still useful even in the
presence of that class if the file is really temporary (meant to be
removed when the QTemporaryFile is destroyed).
Pick-to: 5.15 6.2 6.3
Fixes: QTBUG-103740
Change-Id: Iba16e8ea451b444ab213fffd16f4461f3f972d8c
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
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