Add a QTemporaryFile/Dir (named?) ctor that doesn't expect a placeholder

The problem with QTemporaryFile's scanning for XXXXXX is when the pattern already includes such an instance. Yes, you can safely (after QTBUG-132597) assume that it will always replace the last one, so you can append .XXXXXX and it will always do the correct thing, but if a user relies on the "if the file name doesn't contain XXXXXX, appends it" behaviour of the constructor, then if the filename does contain XXXXXX, it might be replaced at an unexpected place. A version that doesn't scan would also ... well, not have to scan, saving time.