REG: QDirIterator unicode handling broke in Qt 6.8

We suddenly had weird test failures in QtApplicationManager on macOS and it turned out that our testing with a file having a German A-umlaut in its name is handled differently now.

Please see the attached example.

OUTPUT with Qt <= 6.7

FROM UTF8    "xxx.täst" size: 8 umlaut code: e4 73
QDIRITERATOR "xxx.täst" size: 8 umlaut code: e4 73

OUTPUT with Qt dev/6.8

FROM UTF8    "xxx.täst" size: 8 umlaut code: e4 73
QDIRITERATOR "xxx.täst" size: 9 umlaut code: 61 308

As you can see, Qt 6.8 is now reporting the decomposed a-umlaut (0xe4) in composed form (0x61, normal 'a' + 0x308, COMBINING DIAERESIS)

According to the Coin failures, the macOS version doesn't matter. Locally reproduced on macOS 14.2 on an M2.